Vaxart, Inc.

As filed with the Securities and Exchange Commission on May 8**, 2026**

Registration No. 333- ​

UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

WASHINGTON, D.C. 20549

FORMS-1

REGISTRATION STATEMENT

UNDER

THE SECURITIES ACT OF 1933

VAXART, INC.

(Exact name of registrant as specified in its charter)

310 Utah Avenue, Suite 150

South San Francisco, CA 94080

(650) 550-3500

(Address, including zip code, and telephone number, including area code, of registrant’s principal executive offices)​

Steven Lo

Chief Executive Officer

310 Utah Avenue, Suite 150

South San Francisco, CA 94080

(650) 550-3500

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

Copies to:

Faith L. Charles

Thompson Hine LLP

300 Madison Avenue, 27th Floor

New York, NY 10017

(212) 908-3905

Approximate date of commencement of proposed sale to the 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 check the following box. ☒

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. ☐

If this Form is a post-effective amendment filed pursuant to Rule 462(c) 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. ☐

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 number of the earlier effective registration statement for the same offering. ☐

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 Securities Act. ☐

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 WHICH 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.

THE INFORMATION IN THIS PROSPECTUS IS NOT COMPLETE AND MAY BE CHANGED. THE SELLING STOCKHOLDER MAY NOT RESELL THESE SECURITIES UNTIL THE REGISTRATION STATEMENT FILED WITH THE SECURITIES AND EXCHANGE COMMISSION IS DECLARED EFFECTIVE. THIS PROSPECTUS IS NOT AN OFFER TO SELL THESE SECURITIES AND IS NOT SOLICITING AN OFFER TO BUY THESE SECURITIES IN ANY STATE WHERE THE OFFER OR SALE IS NOT PERMITTED. ** **

PRELIMINARY PROSPECTUS

SUBJECT TO COMPLETION DATED May 7**, 2026**

32,914,599 Shares of Common Stock

Vaxart, Inc.

This prospectus relates to the offer and resale of up to 32,914,599 shares of our common stock by Lincoln Park Capital Fund, LLC, which we refer to in this prospectus as “Lincoln Park” or the “selling stockholder.”

The shares of common stock being offered by the selling stockholder consist of:

• up to 32,467,532 shares of common stock that we may elect to issue and sell to Lincoln Park, in our sole discretion from time to time after the date of this prospectus (the “Purchase Shares”), pursuant to a purchase agreement, dated as of April 16, 2026, that we entered into with Lincoln Park, which we refer to in this prospectus as the “Purchase Agreement”, providing for up to $25 million of committed equity financing; and

• 447,067 shares of our common stock that we issued to Lincoln Park on April 16, 2026 as consideration for its irrevocable commitment to purchase our common stock pursuant to the Purchase Agreement (the “Commitment Shares”).

See “The Lincoln Park Transaction” for descriptions of the Purchase Agreement and “Selling Stockholder” for additional information regarding Lincoln Park.

We are not selling any securities under this prospectus and will not receive any of the proceeds from the resale by the selling stockholder of shares of common stock under this prospectus. However, we may receive proceeds of up to $25 million from our sale of Purchase Shares, if any, to Lincoln Park under the Purchase Agreement, from time to time in our discretion after the date the registration statement of which this prospectus is a part is declared effective and the other conditions in the Purchase Agreement have been satisfied.

Lincoln Park may sell the shares of our common stock described in this prospectus in a number of different ways and at varying prices. The price that Lincoln Park will pay for the shares to be resold pursuant to this prospectus will depend upon the timing of sales and will fluctuate based on the trading price of our common stock. Lincoln Park is an “underwriter” within the meaning of Section 2(a)(11) of the Securities Act of 1933, as amended (the “Securities Act”).

The purchase price for the Purchase Shares will be based upon formulas set forth in the Purchase Agreement and described in this prospectus depending on the type of purchase notice we submit to Lincoln Park from time to time. We will pay the expenses incurred in registering the shares of our common stock, including legal and accounting fees. See “Plan of Distribution” beginning on page 130 for more information about how Lincoln Park may sell the shares of common stock being registered pursuant to this prospectus.

Our common stock is quoted on the OTCQX® Best Market (the “OTC”) under the symbol “VXRT.” On May 7, 2026, the closing price per share of our common stock on the OTC was $0.74.

Investing in our common stock is highly speculative and involves a significant degree of risk. Please consider carefully the specific factors set forth under“Risk Factors”** beginning on page 4**** of this prospectus and in our filings with the Securities and Exchange Commission.**

Neither the Securities and Exchange Commission nor any state securities commission has approved or disapproved of these securities or determined if this prospectus is truthful or complete. Any representation to the contrary is a criminal offense.

The date of this prospectus is , 2026.