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As filed with the U.S. Securities and Exchange Commission on February 6,September 20, 2019

Registration No. 333-            333-233717

UNITED STATES
SECURITIES AND EXCHANGE COMMISSION
WASHINGTON, D.C. 20549

AMENDMENT NO. 1
TO

FORM S-1
REGISTRATION STATEMENT
UNDER
THE SECURITIES ACT OF 1933

VAXART, INC.
(Exact name of registrant as specified in its charter)

290 Utah Ave
Suite 200
South San Francisco, California 94080
(650) 550-3500
(Address, including zip code, and telephone number, including area code, of registrant's principal executive offices)

Wouter W. Latour M.D.
President and Chief Executive Officer
290 Utah Ave
Suite 200
South San Francisco, California 94080
(650) 550-3500

(Name, address, including zip code, and telephone number, including area code, of agent for service)

Approximate date of commencement of proposed sale to public:
As soon as practicable after the effective date of this registration statement.

             If any of the securities being registered on this Form are to be offered on a delayed or continuous basis pursuant to Rule 415 under the Securities Act of 1933, as amended, check the following box:    ý

             If this Form is filed to register additional securities for an offering pursuant to Rule 462(b) under the Securities Act, please check the following box and list the Securities Act registration statement number of the earlier effective Registration Statement for the same offering:    o

             If this Form is a post-effective amendment filed pursuant to Rule 462(c) under the Securities Act, please check the following box and list the Securities Act Registration Statement number of the earlier effective Registration Statement for the same offering:    o

             If this Form is a post-effective amendment filed pursuant to Rule 462(d) under the Securities Act, check the following box and list the Securities Act Registration Statement number of the earlier effective Registration Statement for the same offering:    o

             Indicate by check mark whether the registrant is a large accelerated filer, an accelerated filer, a non-accelerated filer, a smaller reporting company or an emerging growth company. See the definitions of "large accelerated filer," "accelerated filer," "smaller reporting company" and "emerging growth company" in Rule 12b-2 of the Exchange Act.

             If an emerging growth company, indicate by check mark if the registrant has elected not to use the extended transition period for complying with any new or revised financial accounting standards provided pursuant to Section 7(a)(2)(B) of the Securities Act of 1933, as amended.    o

CALCULATION OF REGISTRATION FEE

(1)

Estimated solely for purposes of computing the amount of the registration fee pursuant to Rule 457(o) under the Securities Act. The registrant paid $1,394 with the initial filing of this registration statement.

(2)

Includes sharessecurities that the underwriters have the option to purchase.

(3)

The proposed maximum aggregate offering price of the common stock proposed to be sold in the offering will be reduced on a dollar-for-dollar basis based on the aggregate offering price of the pre-funded warrants offered and sold in the offering (plus the aggregate exercise price of the common stock issuable upon exercise of the pre-funded warrants), and as such the proposed aggregate maximum offering price of the common stock and pre-funded warrants (including the common stock issuable upon exercise of the pre-funded warrants), if any, is $            .$11,500,000.

(4)

Represents warrants issuable to H.C. Wainwright & Co., LLCthe underwriters or their designees (the "representative warrants") to purchase a number of shares of common stock equal to 7% of the number of shares of common stock and pre-funded warrants being offered at an exercise price equal to 125% of the public offering price. Resales of the representative warrants on a delayed or continuous basis pursuant to Rule 415 under the Securities Act of 1933, as amended, are registered hereby. See "Underwriting."

(5)

Pursuant to Rule 416, the securities being registered hereunder include such indeterminate number of additional securities as may be issuable to prevent dilution resulting from stock splits, dividends or similar transactions.

             The Registrant hereby amends this Registration Statement on such date or dates as may be necessary to delay its effective date until the Registrant shall file a further amendment that specifically states that this Registration Statement shall thereafter become effective in accordance with Section 8(a) of the Securities Act of 1933, as amended, or until the Registration Statement shall become effective on such date as the Securities and Exchange Commission, acting pursuant to said Section 8(a), may determine.

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The information in this preliminary prospectus is not complete and may be changed. We may not sell these securities or accept an offer to buy these securities until the registration statement filed with the Securities and Exchange Commission is effective. This preliminary prospectus is not an offer to sell these securities and it is not soliciting offers to buy these securities in any state where such offer or sale is not permitted.

PRELIMINARY PROSPECTUS                    SUBJECT TO COMPLETION, DATED FEBRUARY 6, 2019

15,625,000 Shares of Common Stock

Pre-Funded Warrants to Purchase Shares of Common Stock

Common Warrants to Purchase 15,625,000 Shares of Common Stock

          We are offering up to 15,625,000 shares of our common stock.stock and common warrants to purchase an aggregate of 15,625,000 shares of our common stock (and the shares of common stock that are issuable from time to time upon exercise of the common warrants). We are also offering to certain purchasers whose purchase of shares of common stock in this offering would otherwise result in the purchaser, together with its affiliates and certain related parties, beneficially owning more than 4.99% (or, at the election of the purchaser, 9.99%) of our outstanding common stock immediately following the consummation of this offering, the opportunity to purchase, if any such purchaser so chooses, pre-funded warrants, in lieu of shares of common stock that would otherwise result in such purchaser's beneficial ownership exceeding 4.99% (or, at the election of the purchaser, 9.99%) of our outstanding common stock. Each pre-funded warrant will be exercisable for one share of our common stock and will be accompanied by a common warrant to purchase one share of common stock. The purchase price of each pre-funded warrant will be equal to the price at which a share of common stock is sold to the public in this offering, minus $            ,$0.10, and the exercise price of each pre-funded warrant will be $$0.10 per share. The pre-funded warrants will be immediately exercisable and may be exercised at any time until all of the pre-funded warrants are exercised in full. This offering also relates to the shares of common stock issuable upon exercise of the common warrants and any pre-funded warrants sold in this offering. For each pre-funded warrant we sell, the number of shares of common stock we are offering will be decreased on a one-for-one basis. Therefore the number of common warrants sold in this offering will not change as a result of a change in the mix of the shares of our common stock and pre-funded warrants sold. The common warrants will be exercisable immediately and will expire five years from the date of issuance. The shares of common stock and pre-funded warrants, and the accompanying common warrants, can only be purchased together in this offering but will be issued separately and will be immediately separable upon issuance. Our common stock is listed on the Nasdaq Capital Market under the symbol "VXRT." On February 5,September 18, 2019, the last reported sale price of our common stock was $2.22$0.64 per share. The actual public offering price per share of common stock and any pre-funded warrant will be determined between us and the underwriterunderwriters at the time of pricing, and may be at a discount to the current market price. Therefore, the assumed public offering price used throughout this prospectus may not be indicative of the final offering price. There is no established public trading market for the pre-funded warrants and the representativecommon warrants, and we do not expect a market to develop. In addition, we do not intend to apply for a listing of the pre-funded warrants and the representativecommon warrants on any national securities exchange or other nationally recognized trading system.

          Investing in shares of our common stock and pre-funded warrantssecurities involves a high degree of risk. You should carefully read and consider the "Risk Factors" beginning on page 911 of this prospectus before investing.

          Neither the Securities and Exchange Commission nor any state securities commission has approved or disapproved of these securities or passed upon the adequacy or accuracy of this prospectus. Any representation to the contrary is a criminal offense.

(1)

In addition, we have agreed to issue to the underwriters or their designees warrants to purchase a number of shares of common stock equal to 7.0% of the shares of common stock and pre-funded warrants sold in this offering. See "Underwriting" for additional information and a description of the compensation payable to the underwriters.

(2)

The public offering price is $            per share of common stock and $            per pre-funded warrant to purchase a share of common stock.

          We have granted the underwriters the right to purchase up to 2,343,750 additional shares of our common stock and/or common warrants to purchase up to an aggregate of an additional 2,343,750 shares of common stock, in each case at the public offering price, less underwriting discounts and commissions. The underwriters can exercise this right at any time within 30 days from the date of this prospectus. If the underwriters exercise their option to purchase additional shares and/or common warrants in full, we estimate that our netthe total underwriting discounts and commissions payable by us will be $            and the total proceeds to us from this offering, before expenses, will be approximately $            , excluding the proceeds, if any, from the exercise of the representativepre-funded warrants and common warrants.

          We anticipate that delivery of the common stock, and any pre-funded warrants and accompanying common warrants will be made on or about                    , 2019.

Sole Book-Running Manager

H.C. Wainwright & Co.

Manager

CIMArcadia Securities LLC

The date of this prospectus is                        , 2019.

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        We and the underwriters have not authorized anyone to provide any information or to make any representations other than those contained in or incorporated by reference in this prospectus or in any free writing prospectuses prepared by or on behalf of us or to which we have referred you. We take no responsibility for, and can provide no assurance as to the reliability of, any other information that others may give you. This prospectus is an offer to sell only the shares offered hereby, but only under circumstances and in jurisdictions where it is lawful to do so. The information contained in or incorporated by reference in this prospectus is accurate only as of its date regardless of the time of delivery of this prospectus or of any sale of common stock or pre-funded warrants and accompanying common warrants.

        Neither we nor the underwriters have done anything that would permit this offering or possession or distribution of this prospectus in any jurisdiction where action for that purpose is required, other than in the United States. Persons who come into possession of this prospectus and any free writing prospectus in jurisdictions outside the United States are required to inform themselves about and to observe any restrictions as to this offering and the distribution of this prospectus and any free writing prospectus applicable to that jurisdiction.

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RISK FACTORS

        An investment in our securities involves a high degree of risk. You should carefully consider the risks described below as well as the other information in this prospectus and incorporated by reference in this prospectus before making a decision to invest in shares of our common stock or pre-funded warrants and accompanying common warrants, including the risks described under "Risk Factors" in our AnnualQuarterly Report on Form 10-K10-Q for the yearquarter ended December 31, 2018.June 30, 2019. Our business faces significant risks and the risks described below may not be the only risks we face. Additional risks not presently known to us or that we currently believe are immaterial may also significantly impair our business operations. If any of these risks occur, our business, results of operations or financial condition and prospects could be harmed. In that event, the market price of our common stock and the value of the pre-funded warrants could decline, and you could lose all or part of your investment.

Risks Related to this Offering

Management will have broad discretion as to the use of the net proceeds from this offering, and we may not use these proceeds effectively.

        We have not designated any portion of the net proceeds from this offering to be used for any particular purposes. Our management will have broad discretion in the application of the net proceeds from this offering and could spend the proceeds in ways that do not improve our results of operations or enhance the value of our common stock. Accordingly, you will be relying on the judgment of our management with regard to the use of these net proceeds, and you will not have the opportunity, as part of your investment decision, to assess whether the proceeds are being used appropriately. Our failure to apply these funds effectively could have a material adverse effect on our business, delay the development of our products and cause the price of our common stock to decline.

You will experience immediate and substantial dilution.dilution if you purchase securities in this offering.

        The price at which a share of common stock is sold in this offering will exceed the net tangible book value (deficit) per share of our common stock outstanding prior to this offering. Assuming that 15,625,000 shares of our common stock and            pre-funded warrants are sold in this offering, based on an assumed combined public offering price of $$0.64 per share theof common stock and accompanying common warrant (the last reported sale price of our common stock on the Nasdaq Capital Market on September 18, 2019), 2019, and $            per pre-funded warrant, excluding the proceeds, if any, from the exercise of the representative warrants, and after deducting underwriting discounts and commissions and estimated offering expenses payable by us, you will experience immediate dilution of $0.42 per share, representing the difference between the price you pay and our as adjusted net tangible book value (deficit) per share as of December 31, 2018,June 30, 2019, after giving effect to this offering. The exercise of outstanding stock options or warrants, including pre-funded warrants and representative warrants, may result in further dilution of your investment. See the section titled "Dilution" below for a more detailed illustration of the dilution you would incur if you participate in this offering.

Purchasers in this offering may experience additional dilution of their investment in the future.

        We may choose to raise additional capital due to market conditions or strategic considerations even if we believe we have sufficient funds for our current or future operating plans. If additional capital is raised through the sale of equity or convertible debt securities, or perceptions that those sales could occur, the issuance of these securities could result in further dilution to investors purchasing our common stock or pre-funded warrants in this offering or result in downward pressure on the price of our common stock, and our ability to raise capital in the future. In order to raise additional capital, such securities may be at prices that are not the same as the price per share in this offering. We cannot assure you that we will be able to sell shares or other securities in any other offering at a price per share that is equal to or greater than the price per share paid by investors in this offering, and

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investors purchasing shares or other securities in the future could have rights superior to existing stockholders, including investors who purchase securities in this offering. The price per share at which

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we sell additional shares of our common stock or securities convertible into common stock in future transactions may be higher or lower than the price per share in this offering.

There is no public market for the pre-funded warrants or common warrants being offered in this offering.

        There is no established public trading market for the pre-funded warrants or common warrants being offered in this offering, and we do not expect a market to develop. In addition, we do not intend to apply to list the pre-funded warrants or common warrants on any securities exchange or nationally recognized trading system, including the Nasdaq Capital Market. Without an active market, the liquidity of the pre-funded warrants and common warrants will be limited.

Holders of our pre-funded warrants and common warrants will have no rights as a common stockholder until they acquire our common stock.

        Until you acquire shares of our common stock upon exercise of your pre-funded warrants or common warrants, you will have no rights with respect to shares of our common stock issuable upon exercise of your pre-funded warrants or common warrants. Upon exercise of your pre-funded warrants or common warrants, you will be entitled to exercise the rights of a common stockholder only as to matters for which the record date occurs after the exercise date.

The pre-funded warrants and common warrants are speculative in nature.

        Neither the pre-funded warrants nor the common warrants offered hereby confer any rights of common stock ownership on their holders, such as voting rights or the right to receive dividends, but rather merely represent the right to acquire shares of common stock at a fixed price. Specifically, commencing on the date of issuance, holders of the pre-funded warrants may acquire the common stock issuable upon exercise of such warrants at an exercise price of $0.10 per share of common stock and holders of the common warrants may acquire the common stock issuable upon exercise of such warrants at an exercise price of $            per share. Moreover, following this offering, the market value of the pre-funded warrants and common warrants is uncertain and there can be no assurance that the market value of the pre-funded warrants or the common warrants will equal or exceed their public offering price. There can be no assurance that the market price of the common stock will ever equal or exceed the exercise price of the pre-funded warrants or common warrants, and consequently, whether it will ever be profitable for holders of the pre-funded warrants to exercise the pre-funded warrants or the holders of the common warrants to exercise the common warrants.

Our failure to meet the continued listing requirements of the Nasdaq Capital Market could result in a delisting of our common stock.

        Our common stock is listed on the Nasdaq Capital Market, which imposes, among other requirements a minimum bid requirement. Our common stock traded for less than $1.00 for 30 consecutive trading days, and we received notice of this from the Listing Qualifications Staff of The Nasdaq Stock Market LLC on May 22, 2019. Under Nasdaq Listing Rule 5810(c)(3)(A), we were granted a 180 calendar day grace period, or until November 18, 2019, to regain compliance with the minimum bid price requirement. The minimum bid price requirement will be met if our common stock has a minimum closing bid price of at least $1.00 per share for a minimum of 10 consecutive business days during the 180 calendar day grace period. If we do not regain compliance with the Rule by November 18, 2019 but we meet the Nasdaq Capital Market initial inclusion criteria set forth in Nasdaq Listing Rule 5505, except for the minimum $1.00 per share bid price requirement, we will be granted an additional 180-calendar day compliance period. If we do not regain compliance with the Rule by November 18, 2019 and are not eligible for an additional compliance period at that time, the Nasdaq staff will provide written notification to us that our common stock will be delisted. At that time, we may appeal the Nasdaq staff's delisting determination to a Nasdaq Listing Qualifications Panel

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pursuant to the procedures set forth in the applicable Nasdaq Listing Rules. There can be no assurance that we will be able to regain compliance or that Nasdaq will grant us a further extension of time to regain compliance, if necessary.

        The delisting of our common stock from Nasdaq may make it more difficult for us to raise capital on favorable terms in the future, or at all. Such a delisting would likely have a negative effect on the price of our common stock and would impair your ability to sell or purchase our common stock when you wish to do so. Further, if our common stock were to be delisted from the Nasdaq Capital Market, our common stock would cease to be recognized as a covered security and we would be subject to additional regulation in each state in which we offer our securities. Moreover, there is no assurance that any actions that we take to restore our compliance with the Nasdaq minimum bid requirement would stabilize the market price or improve the liquidity of our common stock, prevent our common stock from falling below the Nasdaq minimum bid price required for continued listing again, or prevent future non-compliance with Nasdaq's listing requirements.

        There can be no assurance that we will continue to meet the minimum bid price requirement, or any other requirement in the future. If we fail to meet the minimum bid price requirement, or other applicable Nasdaq listing requirements, including maintaining minimum levels of stockholders' equity or market values of our common stock, our common stock could be delisted. If our common stock were to be delisted, the liquidity of our common stock would be adversely affected, and the market price of our common stock could decrease.

Unless our common stock continues to be listed on a national securities exchange it will become subject to the so-called "penny stock" rules that impose restrictive sales practice requirements.

        If we are unable to maintain the listing of our common stock on Nasdaq or another national securities exchange, our common stock could become subject to the so-called "penny stock" rules if the shares have a market value of less than $5.00 per share. The SEC has adopted regulations that define a penny stock to include any stock that has a market price of less than $5.00 per share, subject to certain exceptions, including an exception for stock traded on a national securities exchange. The SEC regulations impose restrictive sales practice requirements on broker-dealers who sell penny stocks to persons other than established customers and accredited investors. An accredited investor generally is a person whose individual annual income exceeded $200,000, or whose joint annual income with a spouse exceeded $300,000 during the past two years and who expects their annual income to exceed the applicable level during the current year, or a person with net worth in excess of $1.0 million, not including the value of the investor's principal residence and excluding mortgage debt secured by the investor's principal residence up to the estimated fair market value of the home, except that any mortgage debt incurred by the investor within 60 days prior to the date of the transaction shall not be excluded from the determination of the investor's net worth unless the mortgage debt was incurred to acquire the residence. For transactions covered by this rule, the broker-dealer must make a special suitability determination for the purchaser and must have received the purchaser's written consent to the transaction prior to sale. This means that if we are unable maintain the listing of our common stock on a national securities exchange, the ability of stockholders to sell their common stock in the secondary market could be adversely affected.

        If a transaction involving a penny stock is not exempt from the SEC's rule, a broker-dealer must deliver a disclosure schedule relating to the penny stock market to each investor prior to a transaction. The broker-dealer also must disclose the commissions payable to both the broker-dealer and its registered representative, current quotations for the penny stock, and, if the broker-dealer is the sole market-maker, the broker-dealer must disclose this fact and the broker-dealer's presumed control over the market. Finally, monthly statements must be sent disclosing recent price information for the penny stock held in the customer's account and information on the limited market in penny stocks.

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We may be unable to fully utilize our federal net operating loss carryforwards to reduce our income taxes as a result of the changes in corporate ownership caused by this offering.

        Under Section 382 of the Internal Revenue Code, and corresponding provisions of state law, if a corporation undergoes an "ownership change," which occurs if there is a cumulative change in the corporation's equity ownership by certain stockholders that exceeds 50% over a three-year period, the corporation's ability to use its pre-change net operating loss carryforwards and other pre-change tax attributes to offset its post-change income may be limited. It is possible that the change in ownership caused by new investors in this offering, combined with offerings earlier this year and future offerings, will result in a change of ownership for Section 382 purposes. We have previously reported that the Merger that occurred on February 13, 2018, probably resulted in such an ownership change. If an ownership change occurs as a result of this offering, our ability to use our net operating loss tax credit carryforwards may be further materially limited, which could harm our future operating results by increasing our future tax obligations.

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SPECIAL NOTE REGARDING FORWARD-LOOKING STATEMENTS

        This prospectus and the documents we have filed with the Securities and Exchange Commission, or the SEC, that are incorporated by reference contain "forward-looking statements" within the meaning of Section 27A of the Securities Act of 1933, as amended, or the Securities Act, and Section 21E of the Securities Exchange Act of 1934, or the Exchange Act. These statements relate to future events or to our future operating or financial performance and involve known and unknown risks, uncertainties and other factors which may cause our actual results, performance or achievements to be materially different from any future results, performances or achievements expressed or implied by the forward-looking statements. Forward-looking statements may include, but are not limited to, statements about:

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our ability to fund our working capital requirements;



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the amount and timing of royalties received on sales of Relenza and Inavir;



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the timing and costs of our planned clinical trials for our tablet vaccine product candidates, both tablet vaccines and small-molecule antiviral drugs;candidates;



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our ability to obtain and maintain regulatory approval of our product candidates;



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our ability to establish and scale commercial manufacturing capabilities;



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the rate and degree of market acceptance of our products, if any, that are approved;



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our estimates of our expenses, ongoing losses, future revenue, capital requirements and our needs for or ability to obtain additional financing;



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our ability to obtain and maintain intellectual property protection for our product candidates;



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our ability to identify and develop new product candidates and the number and characteristics of product candidates that we pursue;



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our ability to retain and recruit key personnel;



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our planned use of the proceeds from this offering;



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our financial performance;



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our ability to become profitable and generate consistent cash flows to remain profitable; and



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developments and projections relating to our competitors or our industry; and



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our expected use of the net proceeds from this offering.industry.

        In some cases, you can identify forward-looking statements by terms such as "anticipates," "believes," "could," "estimates," "intends," "may," "plans," "potential," "will," "would," or the negative of these terms or other similar expressions. These statements reflect our current views with respect to future events and are based on assumptions and are subject to risks and uncertainties. Given these uncertainties, you should not place undue reliance on these forward-looking statements. We discuss in greater detail many of these risks in the section titled "Risk Factors", in any free writing prospectuses we may authorize for use in connection with this offering, and in our most recent AnnualQuarterly Report on Form 10-K,10-Q, as well as any amendments thereto reflected in subsequent filings with the SEC, which are incorporated by reference into this prospectus in their entirety. Also, these forward-looking statements represent our estimates and assumptions only as of the date of the document containing the applicable statement. Unless required by law, we undertake no obligation to update or revise any forward-looking statements to reflect new information or future events or developments.

        In addition, statements that "we believe" and similar statements reflect our beliefs and opinions on the relevant subject. These statements are based upon information available to us as of the date of this

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prospectus, and while we believe such information forms a reasonable basis for such statements, such information may be limited or incomplete, and our statements should not be read to indicate that we

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have conducted an exhaustive inquiry into, or review of, all potentially available relevant information. These statements are inherently uncertain and investors are cautioned not to unduly rely upon these statements.

        You should read this prospectus, together with the documents we have filed with the SEC that are incorporated by reference and any free writing prospectus that we may authorize for use in connection with this offering completely and with the understanding that our actual future results may be materially different from what we expect. We qualify all of the forward-looking statements in the foregoing documents by these cautionary statements.

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MARKET AND INDUSTRY DATA

        This prospectus and the documents incorporated by reference in this prospectus contain market data and industry statistics and forecasts that are based on independent industry publications and other publicly available information. Although we believe that these sources are reliable, we do not guarantee the accuracy or completeness of this information and we have not independently verified this information. Although we are not aware of any misstatements regarding the market and industry data presented or incorporated by reference in this prospectus, these estimates involve risks and uncertainties and are subject to change based on various factors, including those discussed in the section titled "Risk Factors" and any related free writing prospectus. Accordingly, investors should not place undue reliance on this information.

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USE OF PROCEEDS

        We estimate that our net proceeds from the sale of 15,625,000 shares of common stock in this offering will be approximately $$8.9 million, excluding the proceeds, if any, from the exercise of the pre-funded warrants and representative warrants, and after deducting underwriting discounts and commissions and estimated offering expenses payable by us, based on the sale of                         shares of our common stock in this offering at an assumed combined public offering price of $$0.64 per share of common stock and accompanying common warrant (the last reported sale price of our common stock on the Nasdaq Capital Market on September 18, 2019), 2019)after deducting underwriting discounts and $            per pre-funded warrant.commissions and estimated offering expenses payable by us. If the underwriters exercise their option to purchase 2,343,750 additional shares of common stock together with accompanying common warrants to purchase up to 2,343,750 shares of common stock in full, we estimate that our net proceeds from this offering will be approximately $$10.3 million, excluding the proceeds, if any, from the exercise of the pre-funded warrants and representative warrants and after deducting underwriting discounts and commissions and estimated offering expenses payable by us. We cannot predict when or if the common warrants will be exercised. It is possible that the common warrants may expire and may never be exercised.

        Each $0.50A $0.25 increase (decrease) in the assumed combined public offering price of $$0.64 per share of our common stock and accompanying common warrant (the last reported sale price of our common stock on the Nasdaq Capital Market on ,September 18, 2019) would increase (decrease) the expected net cash proceeds of the offering to us by approximately $             million. Each$3.6 million, assuming that the number of shares offered by us, as set forth on the cover page of this prospectus remains the same, after deducting underwriting discounts and commissions and estimated offering expenses payable by us. An increase (decrease) of 1.0 million shares in the number of shares of common stock offered by us would increase (decrease) the net proceeds to us from this offering by approximately $             million,$595,000, assuming that the assumed combined public offering price of our$0.64 per share of common stock and accompanying common warrant remains the same, and after deducting underwriting discounts and commissions and estimated offering expenses payable by us.

        We currently intend to use the net proceeds from the sale of the shares of our common stock and pre-funded warrants offered by us, if any,this offering to support the clinical and preclinical development of our product candidates, to conduct clinical trials, including a Phase I studystudies with our bivalent norovirus vaccines and a Phase II challenge study with our GI.1 monovalent norovirus vaccine, to support the manufacturing of our vaccines, for these clinical trials and to advance our therapeutic HPV vaccine candidate, and for general corporate and working capital purposes. Accordingly, we retain broad discretion to use of these proceeds.

        Pending the use of the net proceeds from this offering, we intend to invest the net proceeds in investment-grade, interest-bearing instruments.

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DIVIDEND POLICY

        We have never paid or declared any cash dividends on our common stock. We do not anticipate paying any cash dividends on our common stock in the foreseeable future, and we intend to retain all available funds and any future earnings to fund the development and expansion of our business. In addition, covenants in the agreement governing our senior secured credit facility do not allow for the payment of any cash dividends. Any future determination to pay dividends will be at the discretion of our board of directors and will depend upon a number of factors, including our results of operations, financial condition, future prospects, contractual restrictions, restrictions imposed by applicable law and other factors our board of directors deems relevant.

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CAPITALIZATION

        The following table shows our cash and cash equivalents and our capitalization as of December 31, 2018June 30, 2019 on:

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an actual basis; and



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an as adjusted basis, giving further effect to the sale by us of shares of common stock and          pre-funded warrants to purchase15,625,000 shares of common stock in this offering at the assumed combined public offering price of $$0.64 per share of common stock and accompanying warrant (the last reported sale price of our common stock on the Nasdaq Capital Market on September 18, 2019), 2019) and $            per pre-funded warrant, after deducting underwriting discounts and commissions and estimated offering expenses payable by us.

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        The number of shares of common stock in the table above excludes:

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865,1632,166,800 shares issuable upon the exercise of outstanding stock options with a weighted-average exercise price of $8.13$3.19 per share;



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1,646,364 shares issuable upon the exercise of outstanding pre-funded warrants with an exercise price of $0.10 per share;



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10,454,546 shares issuable upon the exercise of outstanding warrants with an exercise price of $1.10 per share;



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636,364 shares issuable upon the exercise of outstanding warrants with an exercise price of $1.375 per share;



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84,000 shares issuable upon the exercise of outstanding warrants with an exercise price of $3.125 per share;



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10,914 shares issuable upon the exercise of an outstanding warrant with an exercise price of $22.99 per share; and



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223,377186,410 shares reserved for future issuance under our 20162019 Equity Incentive Plan.

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DILUTION

        If you purchase securities in this offering, your interest will be diluted to the extent of the difference between the combined public offering price per share and the as adjusted net tangible book value (deficit) per share of our common stock after this offering, assuming no value is attributed to the pre-funded warrants, and such pre-funded warrants are accounted for and classified as equity.

        As of December 31, 2018,June 30, 2019, our net tangible book value (deficit) was $(8.2)$(2.1) million, or $(1.14)$(0.13) per share. Net tangible book value (deficit) per share is total tangible assets less total liabilities divided by the total number of outstanding shares of common stock.

        After giving effect to the sale of 15,625,000 shares of common stock and pre-fundedaccompanying common warrants, in this offering at an assumed combined public offering price of $$0.64 per share and accompanying common warrant (the last reported sale price of our common stock as reported on the Nasdaq Capital Market on September 18, 2019), 2019) and $            per pre-funded warrant, and the exercise of the pre-funded warrants, but excluding the proceeds, if any, from the exercise of the representative warrants, and after deducting underwriting discounts and commissions and estimated offering expenses payable by us, our as adjusted net tangible book value (deficit) as of December 31, 2018,June 30, 2019, would have been $$6.8 million, or $$0.22 per share. This represents an immediate increase in as adjusted net tangible book value (deficit) of $$0.35 per share to our existing stockholders and immediate dilution in net tangible book value (deficit) of $$0.42 per share to investors participating in this offering. The following table illustrates this dilution per share to investors participating in this offering:

        Each $0.50$0.25 increase (decrease) in the assumed combined public offering price of $$0.64 per share of common stock and accompanying common warrant would increase (decrease), respectively, our as adjusted net tangible book value (deficit) after this offering by $             million, or $$0.12 per share, and the dilution per share to new investors by $$0.13 per share, assuming that the number of shares of common stock offered by us, as set forth above, remains the same, excluding the proceeds, if any, from the exercise of the pre-funded warrants and representative warrants issued in this offering, and after deducting underwriting discounts and commissions and estimated offering expenses payable by us. We may also increase or decrease the number of shares of common stock we are offering from the assumed number of shares of common stock set forth above.offering. An increase (decrease) of 1.0 million shares of common stock in the number of shares of common stock offered by us from the assumed number of shares of common stock set forth above would increase (decrease) our as adjusted net tangible book value (deficit) after this offering by $             million, or $$0.01 per share, and the dilution per share to new investors would (decrease) increase by $$0.01 per share, assuming that the assumed public offering price of the common stock remains the same excluding the proceeds, if any, from the exercise of the pre-funded warrants and the representative warrants, and after deducting underwriting discounts and commissions and estimated offering expenses payable by us.

        The information discussed above is illustrative only and will adjust based on the actual combined public offering price of the common stock and accompanying warrant, the actual number of shares that we offer in this offering, and other terms of this offering determined at pricing. The discussion and table above assume (i) no sale of pre-funded warrants, which, if sold, would reduce the number of shares of common stock that we are offering on a one-for-one basis, (ii) no exercise of the underwriter's option to purchase up to an additional 2,343,750 shares of common stock and/or common warrants to purchase up to an additional 2,343,750 shares of our common stock and (iii) no exercise of common warrants accompanying the shares of common stock and pre-funded warrants, if any, sold in this offering.

        If the underwriters exercise in full their option to purchase up to 2,343,750 additional shares of common stock together with accompanying common warrants to purchase up to an additional 2,343,750 shares of common stock, our as adjusted net tangible book value after this offering would be $0.24 per

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share, representing an increase in as adjusted net tangible book value of $0.37 per share to existing stockholders and immediate dilution in net tangible book value of $0.40 per share to new investors in this offering.

        If investors in this offering exercise in full the common warrants for 15,625,000 shares of common stock offered hereby for cash at an assumed exercise price of $0.64 per share (the last reported sale price of our common stock on the Nasdaq Capital Market on September 18, 2019), our as adjusted net tangible book value after this offering would be $0.36 per share, representing an increase in as adjusted net tangible book value of $0.49 per share and immediate dilution in net tangible book value of $0.28 per share to new investors in this offering.

        The number of shares of common stock to be outstanding after this offering is based on 7,141,18915,785,735 shares of common stock outstanding as of December 31,June 30, 2018, and excludes:

•

865,1632,166,800 shares issuable upon the exercise of outstanding stock options with a weighted-average exercise price of $8.13$3.19 per share;



•

1,646,364 shares issuable upon the exercise of outstanding pre-funded warrants with an exercise price of $0.10 per share;



•

10,454,546 shares issuable upon the exercise of outstanding warrants with an exercise price of $1.10 per share;



•

636,364 shares issuable upon the exercise of outstanding warrants with an exercise price of $1.375 per share;



•

84,000 shares issuable upon the exercise of outstanding warrants with an exercise price of $3.125 per share;



•

10,914 shares issuable upon the exercise of an outstanding warrant with an exercise price of $22.99 per share; and



•

223,377186,410 shares reserved for future issuance under our 20162019 Equity Incentive Plan.

        To the extent that any outstanding options or pre-funded warrants are exercised, there will be further dilution to new investors.

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PRINCIPAL STOCKHOLDERS

        The following table sets forth, as of December 31, 2018,June 30, 2019, information regarding beneficial ownership of our common stock by:

•

each stockholder known by us to beneficially own more than 5% of our outstanding common stock;



•

each of our current named executive officers as set forth in our Annual Report on Form 10-K for the year ended December 31, 2018;officers;



•

each of our directors; and



•

all of our current executive officers and directors as a group.

        Beneficial ownership is determined according to the rules of the SEC and generally means that a person has beneficial ownership of a security if he, she or it possesses sole or shared voting or investment power of that security, including options and warrants that are currently exercisable or exercisable within 60 days of December 31, 2018.June 30, 2019. Except as indicated by the footnotes below, we believe, based on the information furnished to us, that the persons named in the table below have sole voting and investment power with respect to all shares of common stock shown that they beneficially own.

        Our calculation of the percentage of beneficial ownership prior tobefore this offering is based on 7,141,18915,785,735 shares of our common stock outstanding as of December 31, 2018.June 30, 2019. We have based our calculation of the percentage of beneficial ownership after this offering on 31,410,735 shares of our common stock to be outstanding immediately after the closing of this offering, assuming no sale of any pre-funded warrants and assuming no exercise of the pre-fundedany common warrants or theany representative warrants, issued in this offering and assuming no exercise by the underwriters of their option to purchase additional shares.shares and/or common warrants.

        Common stock subject to stock options, pre-funded warrants and common warrants currently exercisable or exercisable within 60 days of December 31, 2018,June 30, 2019, are deemed to be outstanding for computing the percentage ownership of the person holding these optionssecurities and the percentage ownership of any group of which the holder is a member but are not deemed outstanding for computing the percentage of any other person.

        Unless otherwise noted below, the address for each of the stockholders in the table below is c/o Vaxart, Inc., 290 Utah Ave, Suite 200, South San Francisco, California 94080.

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DESCRIPTION OF CAPITAL STOCK

        The following summary description of our capital stock is based on the provisions of our amended and restated certificate of incorporation and amended and restated bylaws and the applicable provisions of the Delaware General Corporation Law. This information is qualified entirely by reference to the applicable provisions of our amended and restated certificate of incorporation, bylaws and the Delaware General Corporation Law. For information on how to obtain copies of our amended and restated certificate of incorporation and bylaws, which are exhibits to the registration statement of which this prospectus is a part, see the sections titled "Where You Can Find Additional Information" and "Incorporation of Certain Information by Reference" in this prospectus.

General

        Our authorized capital stock consists of (i) 200,000,000100,000,000 shares of common stock, par value $0.10 per share and (ii) 5,000,000 shares of preferred stock, par value $0.10 per share.

        As of December 31, 2018,June 30, 2019, there were 7,141,18915,785,735 shares of common stock issued and outstanding, and no shares of preferred stock outstanding.

        The following is a summary of the material provisions of the common stock and preferred stock provided for in our amended and restated certificate of incorporation and amended and restated bylaws.

Common Stock

Voting

        Our common stock is entitled to one vote for each share held of record on all matters submitted to a vote of the stockholders, except that directors will be elected by a plurality of votes cast. Accordingly, the holders of a majority of the shares of common stock entitled to vote in any election of directors are able to elect all of the directors standing for election, if they so choose.

Dividends

        Subject to preferences that may be applicable to any then outstanding preferred stock, the holders of common stock are entitled to receive dividends, if any, as may be declared from time to time by our board of directors out of legally available funds. We have never paid cash dividends and have no present intention to pay cash dividends.

Liquidation

        In the event of a liquidation, dissolution or winding up, holders of our common stock will be entitled to share ratably in the net assets legally available for distribution to stockholders after the payment of all of our debts and other liabilities, subject to the satisfaction of any liquidation preference granted to the holders of any outstanding shares of preferred stock.

Rights and Preferences

        Holders of our common stock have no preemptive, conversion or subscription rights, and there are no redemption or sinking fund provisions applicable to our common stock. The rights, preferences and privileges of the holders of our common stock are subject to, and may be adversely affected by, the rights of the holders of shares of any series of our preferred stock that we may designate and issue in the future.

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Fully Paid and Nonassessable

        All of our outstanding shares of common stock are fully paid and nonassessable.

Preferred Stock

        Our board of directors has the authority, without further action by the stockholders, to issue up to 5,000,000 shares of preferred stock in one or more series, to establish from time to time the number of shares to be included in each such series, to fix the rights, preferences and privileges of the shares of each wholly unissued series and any qualifications, limitations or restrictions thereon and to increase or decrease the number of shares of any such series, but not below the number of shares of such series then outstanding.

        Our board of directors may authorize the issuance of preferred stock with voting or conversion rights that could adversely affect the voting power or other rights of the holders of the common stock. The issuance of preferred stock, while providing flexibility in connection with possible acquisitions and other corporate purposes, could, among other things, have the effect of delaying, deferring or preventing a change in our control that may otherwise benefit holders of our common stock and may adversely affect the market price of the common stock and the voting and other rights of the holders of common stock. As of December 31, 2018,June 30, 2019, there were no shares of preferred stock outstanding and we have no current plans to issue any shares of preferred stock.

Anti-Takeover Effects of Provisions of Our Charter Documents and Delaware Law

Delaware Anti-Takeover Law

        We are subject to Section 203 of the DGCL, or Section 203. Section 203 generally prohibits a public Delaware corporation from engaging in a "business combination" with an "interested stockholder" for a period of three years after the date of the transaction in which the person became an interested stockholder, unless:

•

prior to the date of the transaction, the board of directors of the corporation approved either the business combination or the transaction which resulted in the stockholder becoming an interested stockholder;



•

the interested stockholder owned at least 85% of the voting stock of the corporation outstanding upon consummation of the transaction, excluding for purposes of determining the number of shares outstanding (1) shares owned by persons who are directors and also officers and (2) shares owned by employee stock plans in which employee participants do not have the right to determine confidentially whether shares held subject to the plan will be tendered in a tender or exchange offer; or



•

on or subsequent to the consummation of the transaction, the business combination is approved by the board and authorized at an annual or special meeting of stockholders, and not by written consent, by the affirmative vote of at least 66^2/3% of the outstanding voting stock which is not owned by the interested stockholder.



•

Section 203 defines a business combination to include:



•

any merger or consolidation involving the corporation and the interested stockholder;



•

any sale, transfer, pledge or other disposition involving the interested stockholder of 10% or more of the assets of the corporation;



•

subject to exceptions, any transaction involving the corporation that has the effect of increasing the proportionate share of the stock of any class or series of the corporation beneficially owned by the interested stockholder;

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subject to exceptions, any transaction that results in the issuance or transfer by the corporation of any stock of the corporation to the interested stockholder; and



•

the receipt by the interested stockholder of the benefit of any loans, advances, guarantees, pledges or other financial benefits provided by or through the corporation.

        In general, Section 203 defines an interested stockholder as any entity or person beneficially owning 15% or more of the outstanding voting stock of the corporation and any entity or person affiliated with or controlling or controlled by the entity or person.

Certificate of Incorporation and Bylaws

        Provisions of our certificate of incorporation and bylaws may delay or discourage transactions involving an actual or potential change-in-control or change in our management, including transactions in which stockholders might otherwise receive a premium for their shares or transactions that our stockholders might otherwise deem to be in their best interests. Therefore, these provisions could adversely affect the price of our common stock. Among other things, our certificate of incorporation and bylaws:

•

permit our board of directors to issue up to 5,000,000 shares of preferred stock, with any rights, preferences and privileges as they may designate (including the right to approve an acquisition or other change in control);



•

provide that the authorized number of directors may be changed only by resolution adopted by a majority of the board of directors;



•

provide that all vacancies, including newly created directorships, may, except as otherwise required by law or subject to the rights of holders of preferred stock as designated from time to time, be filled by the affirmative vote of a majority of directors then in office, even if less than a quorum;



•

require that any action to be taken by our stockholders must be effected at a duly called annual or special meeting of stockholders or by action taken by written consent;



•

provide that stockholders seeking to present proposals before a meeting of stockholders or to nominate candidates for election as directors at a meeting of stockholders must provide notice in writing in a timely manner and also specify requirements as to the form and content of a stockholder's notice; and



•

provide that special meetings of our stockholders may be called only by the chairman of the board, the president or by our board of directors pursuant to a resolution adopted by a majority of the total number of authorized directors (whether or not there exist any vacancies).

Nasdaq Capital Market Listing

        Our common stock is listed on the Nasdaq Capital Market under the symbol "VXRT."

Transfer Agent and Registrar

        The transfer agent and registrar for our common stock is American Stock Transfer & Trust Company, LLC. The transfer agent and registrar's address is 6201 15th Avenue, Brooklyn, New York 11219.

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DESCRIPTION OF SECURITIES WE ARE OFFERING

        We are offering 15,625,000 shares of our common stock and/or pre-funded warrants and pre-fundedaccompanying common warrants to purchase up to 15,625,000 shares of our common stock. Each share of common stock or pre-funded warrant is being sold together with a common warrant to purchase one share of common stock. The shares of common stock, pre-funded warrants and pre-fundedcommon warrants will be issued separately. We are also registering the shares of common stock issuable from time to time upon exercise of the pre-funded warrants and common warrants offered hereby.

Common Stock

        The material terms and provisions of our common stock and each other class of our securities which qualifies or limits our common stock are described under the caption "Description of Capital Stock" in this prospectus.

Pre FundedPre-Funded Warrants

        The following summary of certain terms and provisions of pre-funded warrants that are being offered hereby is not complete and is subject to, and qualified in its entirety by, the provisions of the pre-funded warrant, the form of which is filed as an exhibit to the registration statement of which this prospectus forms a part. Prospective investors should carefully review the terms and provisions of the form of pre-funded warrant for a complete description of the terms and conditions of the pre-funded warrants.

        Duration and Exercise Price.    Each pre-funded warrant offered hereby will have an initial exercise price per share equal to $0.10. The pre-funded warrants will be immediately exercisable and may be exercised at any time until the pre-funded warrants are exercised in full. The exercise price and number of shares of common stock issuable upon exercise is subject to appropriate adjustment in the event of stock dividends, stock splits, reorganizations or similar events affecting our common stock and the exercise price. The pre-funded warrants will be issued separately from the accompanying common warrants, and may be transferred separately immediately thereafter.

        Exercisability.    The pre-funded warrants will be exercisable, at the option of each holder, in whole or in part, by delivering to us a duly executed exercise notice accompanied by payment in full for the number of shares of our common stock purchased upon such exercise (except in the case of a cashless exercise as discussed below). Purchasers of the pre-funded warrants in this offering may elect to deliver their exercise notice following the pricing of the offering and prior to the issuance of the pre-funded warrants at closing to have their pre-funded warrants exercised immediately upon issuance and receive shares of common stock underlying the pre-funded warrants upon closing of this offering. A holder (together with its affiliates) may not exercise any portion of the pre-funded warrant to the extent that the holder would own more than 4.99% of the outstanding common stock immediately after exercise, except that upon at least 61 days' prior notice from the holder to us, the holder may increase the amount of ownership of outstanding stock after exercising the holder's pre-funded warrants up to 9.99% of the number of shares of our common stock outstanding immediately after giving effect to the exercise, as such percentage ownership is determined in accordance with the terms of the pre-funded warrants. Purchasers of pre-funded warrants in this offering may also elect prior to the issuance of the pre-funded warrants to have the initial exercise limitation set at 9.99% of our outstanding common stock. No fractional shares of common stock will be issued in connection with the exercise of a pre-funded warrant. In lieu of fractional shares, we will either pay the holder an amount in cash equal to the fractional amount multiplied by the exercise price or round up to the next whole share.

        Cashless Exercise.    If, at the time a holder exercises its pre-funded warrants, a registration statement registering the issuance of the shares of common stock underlying the pre-funded warrants under the Securities Act is not then effective or available, then in lieu of making the cash payment otherwise contemplated to be made to us upon such exercise in payment of the aggregate exercise price, the holder may elect instead to receive upon such exercise (either in whole or in part) the net

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number of shares of common stock determined according to a formula set forth in the pre-funded warrants.

        Transferability.    Subject to applicable laws, a pre-funded warrant may be transferred at the option of the holder upon surrender of the pre-funded warrant to us together with the appropriate instruments of transfer.

        Exchange Listing.    There is no trading market available for the pre-funded warrants on any securities exchange or nationally recognized trading system. We do not intend to list the pre-funded warrants on any securities exchange or nationally recognized trading system.

        Right as a Stockholder.    Except as otherwise provided in the pre-funded warrants or by virtue of such holder's ownership of shares of our common stock, the holders of the pre-funded warrants do not have the rights or privileges of holders of our common stock, including any voting rights, until they exercise their pre-funded warrants.

        Fundamental Transaction.    In the event of a fundamental transaction, as described in the pre-funded warrants and generally including any reorganization, recapitalization or reclassification of our common stock, the sale, transfer or other disposition of all or substantially all of our properties or assets, our consolidation or merger with or into another person, the acquisition of more than 50% of our outstanding common stock, or any person or group becoming the beneficial owner of 50% of the voting power represented by our outstanding common stock, the holders of the pre-funded warrants will be entitled to receive upon exercise of the pre-funded warrants the kind and amount of securities, cash or other property that the holders would have received had they exercised the pre-funded warrants immediately prior to such fundamental transaction.

Common Warrants

The following summary of certain terms and provisions of common warrants that are being offered hereby is not complete and is subject to, and qualified in its entirety by, the provisions of the common warrants, the form of which is filed as an exhibit to the registration statement of which this prospectus forms a part. Prospective investors should carefully review the terms and provisions of the form of common warrant for a complete description of the terms and conditions of the common warrants.

        Duration and Exercise Price.    Each common warrant offered hereby will have an initial exercise price per share equal to $            . The common warrants will be immediately exercisable and will expire on the fifth anniversary of the original issuance date. The exercise price and number of shares of common stock issuable upon exercise is subject to appropriate adjustment in the event of stock dividends, stock splits, reorganizations or similar events affecting our common stock and the exercise price. The common warrants will be issued separately from the common stock, and may be transferred separately immediately thereafter. A common warrant to purchase one share of our common stock will be issued for every one share of common stock or pre-funded warrant purchased in this offering.

        Exercisability.    The common warrants will be exercisable, at the option of each holder, in whole or in part, by delivering to us a duly executed exercise notice accompanied by payment in full for the number of shares of our common stock purchased upon such exercise (except in the case of a cashless exercise as discussed below). A holder (together with its affiliates) may not exercise any portion of the common warrant to the extent that the holder would own more than 4.99% of the outstanding common stock immediately after exercise, except that upon at least 61 days' prior notice from the holder to us, the holder may increase the amount of ownership of outstanding stock after exercising the holder's common warrants up to 9.99% of the number of shares of our common stock outstanding immediately after giving effect to the exercise, as such percentage ownership is determined in accordance with the terms of the common warrants. Purchasers in this offering may also elect prior to the issuance of the

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common warrants to have the initial exercise limitation set at 9.99% of our outstanding common stock. No fractional shares of common stock will be issued in connection with the exercise of a common warrant. In lieu of fractional shares, we will either pay the holder an amount in cash equal to the fractional amount multiplied by the exercise price or round up to the next whole share.

        Cashless Exercise.    If, at the time a holder exercises its common warrants, a registration statement registering the issuance of the shares of common stock underlying the common warrants under the Securities Act is not then effective or available and an exemption from registration under the Securities Act is not available for the issuance of such shares, then in lieu of making the cash payment otherwise contemplated to be made to us upon such exercise in payment of the aggregate exercise price, the holder may elect instead to receive upon such exercise (either in whole or in part) the net number of shares of common stock determined according to a formula set forth in the common warrants.

        Transferability.    Subject to applicable laws, a common warrant may be transferred at the option of the holder upon surrender of the common warrant to us together with the appropriate instruments of transfer.

        Exchange Listing.    There is no trading market available for the common warrants on any securities exchange or nationally recognized trading system. We do not intend to list the common warrants on any securities exchange or nationally recognized trading system.

        Right as a Stockholder.    Except as otherwise provided in the common warrants or by virtue of such holder's ownership of shares of our common stock, the holders of the common warrants do not have the rights or privileges of holders of our common stock, including any voting rights, until they exercise their common warrants.

        Fundamental Transaction.    In the event of a fundamental transaction, as described in the common warrants and generally including any reorganization, recapitalization or reclassification of our common stock, the sale, transfer or other disposition of all or substantially all of our properties or assets, our consolidation or merger with or into another person, the acquisition of more than 50% of our outstanding common stock, or any person or group becoming the beneficial owner of 50% of the voting power represented by our outstanding common stock, the holders of the common warrants will be entitled to receive upon exercise of the common warrants the kind and amount of securities, cash or other property that the holders would have received had they exercised the common warrants immediately prior to such fundamental transaction. Notwithstanding the foregoing, in the event of a fundamental transaction, the holders will have the option, which may be exercised within 30 days after the consummation of the fundamental transaction, to require us or our successor entity to purchase the common warrants from the holder by paying to the holder an amount of cash equal to the Black Scholes value of the remaining unexercised portion of the common warrant on the date of the consummation of the fundamental transaction. However, if the fundamental transaction is not within our control, including not approved by our board of directors, the holder will only be entitled to receive from us or our successor entity, as of the date of consummation of such fundamental transaction, the same type or form of consideration (and in the same proportion), at the Black Scholes value of the unexercised portion of the common warrant, that is being offered and paid to the holders of common stock in connection with the fundamental transaction, whether that consideration be in the form of cash, stock or any combination thereof, or whether the holders of common stock are given the choice to receive from among alternative forms of consideration in connection with the fundamental transaction.

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UNDERWRITING

        We have entered into an underwriting agreement with H.C. Wainwright & Co., LLC as the sole book-running manager of this offering. Subject to the terms and conditions of the underwriting agreement, we have agreed to sell to the underwriters, and the underwriters have agreed to purchase from us, 15,625,000 shares of our common stock and pre-funded warrants.warrants and accompanying common warrants to purchase 15,625,000 shares of our common stock. Our common stock is listed on the Nasdaq Capital Market under the symbol "VXRT"."VXRT."

        Pursuant to the terms and subject to the conditions contained in the underwriting agreement, we have agreed to sell to the underwriters named below, and the underwriters have agreed to purchase from us, the respective number of shares of common stock, pre-funded warrants and pre-fundedcommon warrants to purchase common stock set forth opposite their name below:

        The underwriting agreement provides that the obligation of the underwriters to purchase the shares of common stock and/or pre-funded warrants and common warrants to purchase shares of common stock offered by this prospectus is subject to certain conditions. The underwriters are obligated to purchase all of the shares of common stock and/or pre-funded warrants and common warrants to purchase shares of our common stock offered hereby if any of the securities are purchased, other than those shares covered by the option to purchase additional shares and/or common warrants described below.

Option to Purchase Additional SharesSecurities

        We have granted the underwriters an option to purchase additional shares.securities. This option, which is exercisable for up to 30 days after the date of this prospectus, permits the underwriters to purchase up to 2,343,750 shares of common stock at a price of $            per share, and/or common warrants exercisable for up to 2,343,750 shares of common stock at a price of $            per common warrant, less underwriting discounts and commissions.

Discounts, Commissions and Expenses

        The underwriters propose to offer the shares of common stock and/orand pre-funded warrants and accompanying common warrants to purchase shares of our common stock pursuant to the underwriting agreement to the public at the combined public offering price set forth on the cover page of this prospectus and to certain dealers at that price less a concession not in excess of $            per share or $        per pre-funded warrant, based on the combined public offering price per share or pre-fundedand accompanying common warrant set forth on the cover page of this prospectus. After this offering, the public offering price and concession may be changed by the underwriters. No such change shall change the amount of proceeds to be received by us as set forth on the cover page of this prospectus.

        In connection with the sale of the common stock and/orand pre-funded warrants and accompanying common warrants to purchase shares of our common stock to be purchased by the underwriters, the underwriters will be deemed to have received compensation in the form of underwriting discounts and commissions. The underwriting discounts and commissions will be 7% of the gross proceeds of this offering, or $            per share of common stock and accompanying common warrant or per pre-funded warrant and accompanying common warrant.

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        The following table shows underwriting discounts and commissions payable to the underwriters by us in connection with this offering:

        We have also agreed to reimburse H.C. Wainwright & Co., LLC for reasonable out-of-pocket expenses, including legal fees and expenses, of up to $110,000.$75,000. We estimate the total expenses payable by us for this offering will be approximately $600,000,$400,000, which amount excludes underwriting discounts and commissions.

Representative Warrants

        In addition, we have agreed to issue to H.C. Wainwright & Co., LLCthe underwriters or their designees warrants to purchase up to 1,257,812 shares of common stock (which represents 7% of the aggregate number of shares of common stock sold in this offering (including the number of shares of common stock issuable upon exercise of the pre-funded warrants and the underwriters' option to purchase additional shares of common stock if exercised) at an assumed exercise price of $            per share of common stock (representing 125% of the combined public offering price per share of common stock to be sold in this offering), exercisable for. The warrants will each have a term of five years from the effective date of the underwriting agreement.registration statement of which this prospectus forms a part. Pursuant to the Financial Industry Regulatory Authority, Inc., or FINRA, Rule 5110(g), the warrants and any shares of common stock issued upon exercise of the warrants may not be sold, transferred, assigned, pledged or hypothecated, or be the subject of any hedging, short sale, derivative, put or call transaction that would result in the effective economic disposition of the securities by any person for a period of 180 days immediately following the date of effectiveness or commencement of sales of this offering, except the transfer of any security: (i) by operation of law or by reason of our reorganization; (ii) to any FINRA member firm participating in the offering and the officers or partners thereof, if all securities so transferred remain subject to the lock-up restriction set forth above for the remainder of the time period; (iii) if the aggregate amount of our securities held by the underwriters or related persons do not exceed 1% of the securities being offered; (iv) that is beneficially owned on a pro-rata basis by all equity owners of an investment fund, provided that no participating member manages or otherwise directs investments by the fund and the participating members in the aggregate do not own more than 10% of the equity in the fund; or (v) the exercise or conversion of any security, if all securities remain subject to the lock-up restriction set forth above for the remainder of the time period.

Right of First Refusal

        We have also granted H.C. Wainwright & Co., LLC certain rights of first refusal to act as an underwriter or placement agent for a period of twelve months following the closing of this offering.until April 2020.

Indemnification

        Pursuant to the underwriting agreement, we have agreed to indemnify the underwriters against certain liabilities, including liabilities under the Securities Act, or to contribute to payments that the underwriter or such other indemnified parties may be required to make in respect of those liabilities.

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Determination of Offering Price

        The actual offering price of the securities we are offering will be negotiated between us and the underwriters based on the trading of our shares of common stock prior to the offering, among other things, and may be at a discount to the current market price.

Lock-Up Agreements

        We have agreed not to (i) offer, pledge, issue, sell, contract to sell, purchase, contract to purchase, lend or otherwise transfer or dispose of, directly or indirectly, any shares of our common stock or any securities convertible into or exercisable or exchangeable for our common stock; (ii) enter into any swap or other arrangement that transfers, in whole or in part, any of the economic consequences of ownership of shares of common stock; or (iii) file any registration statement with the SEC relating to the offering of any shares of our common stock or any securities convertible into or exercisable or exchangeable for shares of our common stock, without the prior written consent of H.C. Wainwright & Co., LLC for a period of 90 days following the date of this prospectus. This consent may be given at any time without public notice. These restrictions on future issuances are subject to exceptions, including for (i) the issuance of shares of our common stock in this offering and shares of our common stock underlying the pre-funded warrants, sold in this offering,common warrants and representative warrants, (ii) the issuance of shares of our common stock upon the exercise of outstanding options or pursuant to certain other rights, (iii) the issuance of shares of our common stock or options to acquire shares of our common stock pursuant to our existing equity incentive plans, and (iv) the filing of one or more registration statements on Form S-8 with respect to shares of our common stock underlying our equity incentive plans from time to time.

        In addition, subject to certain limited circumstances, each of our directors and executive officers, and our principal stockholder, has entered into a lock-up agreement with the underwriters. Under the lock-up agreements, the directors, executive officers and this stockholder may not, directly or indirectly, sell, offer to sell, contract to sell, or grant any option for the sale (including any short sale), grant any security interest in, pledge, hypothecate, hedge, establish an open "put equivalent position" (within the meaning of Rule 16a-1(h) under the Securities Exchange Act of 1934, as amended, or the Exchange Act), or otherwise dispose of, or enter into any transaction which is designed to or could be expected to result in the disposition of, any shares of our common stock or securities convertible into or exchangeable for shares of our common stock, or publicly announce any intention to do any of the foregoing, without the prior written consent of H.C. Wainwright & Co., LLC, for a period of 90 days from the date of this prospectus. This consent may be given at any time without public notice.

Electronic Distribution

        This prospectus may be made available in electronic format on websites or through other online services maintained by the underwriters or by their affiliates. In those cases, prospective investors may view offering terms online and prospective investors may be allowed to place orders online. Other than this prospectus in electronic format, the information on the underwriter's websites or our website and any information contained in any other websites maintained by the underwriter or by us is not part of this prospectus or the registration statement of which this prospectus forms a part, has not been approved and/or endorsed by us or the underwriter in its capacity as underwriter, and should not be relied upon by investors.

Table of Contents

Price Stabilization, Short Positions and Penalty Bids

        The underwriters may engage in syndicate covering transactions, stabilizing transactions and penalty bids or purchases for the purpose of pegging, fixing or maintaining the price of our shares of common stock:

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Syndicate covering transactions involve purchases of securities in the open market after the distribution has been completed in order to cover syndicate short positions. Such a naked short position would be closed out by buying securities in the open market. A naked short position is more likely to be created if the underwriter is concerned that there could be downward pressure on the price of the securities in the open market after pricing that could adversely affect investors who purchase in the offering.



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Stabilizing transactions permit bids to purchase the underlying security so long as the stabilizing bids do not exceed a specific maximum.