Altimmune Inc美股招股说明书(2026-04-22版)

The information in this preliminary prospectus supplement and the accompanying prospectus is notcompleteand may be changed.This preliminary prospectus supplement and the accompanyingprospectuses are not an offer to sell these securities and are not soliciting an offer to buy these securities inany state or other jurisdiction where the offer or sale is not permitted. Subject to Completion, dated April 22, 2026 (to Prospectus dated December 5, 2025 and Prospectus dated March 13, 2025) Shares of Common StockPre-Funded Warrants to PurchaseShares of Common Stock We are offeringshares of our common stock, par value $0.0001 per share, accompanying commonstock warrants to purchase up toshare of our common stock, and, in lieu of common stock to certaininvestors that so choose, pre-funded warrants to purchase up toshares of our common stock,pursuant to this prospectus supplement and the accompanying prospectuses. Each share of our commonstock, or pre-funded warrant in lieu thereof, is being sold together with the common stock warrants, eachto purchase one share of our common stock (or pre-funded warrants in lieu thereof). Each pre-fundedwarrant is exercisable for one share of common stock. The shares of our common stock (or pre-funded warrants) and common stock warrants are immediatelyseparable and will be issued separately, but will be purchased together in this offering. The common stockwarrants are exercisable at any time after their original issuance and may be exercised until the date that isthe earlier of (i) the fifth anniversary of the original issue date and (ii) 45 days following the Company’spublicannouncement of a successful data readout of Phase 3 trial of pemvidutide in metabolicdysfunction-associated steatohepatitis (“MASH”). The common stock warrants will have an exercise priceof $per share of our common stock, subject to adjustment as described elsewhere in this prospectussupplement. The purchase price of each pre-funded warrant will equal the price per share at which shares of commonstock are being sold to the public in this offering less $0.001, which is the exercise price of each pre-funded warrant. This prospectus supplement also relates to the offering of the shares of common stockissuable upon exercise of such pre-funded warrants and common stock warrants. The pre-funded warrantsdo not expire, and each pre-funded warrant will be exercisable at any time after the date of issuance,subject to an ownership limitation. Our common stock is listed on The Nasdaq Global Market under the symbol “ALT.” On April 21, 2026,the last reported sale price of our common stock on The Nasdaq Global Market, was $3.41 per share.There is no established public trading market for the pre-funded warrants or the common stock warrants,and we do not expect a market to develop. We do not intend to list the pre-funded warrants or the commonstock warrants on The Nasdaq Global Market or any other national securities exchange or nationallyrecognized trading system. We are a “smaller reporting company” under U.S. federal securities laws and as such are subject toreduced public company reporting requirements. Investing in our securities involves a high degree of risk. See “Risk Factors” beginning on pageS-6of this prospectus supplement and other similar headings in the documents that are incorporated byreference into this prospectus supplement and the accompanying base prospectuses for a discussionof information that should be considered in connection with an investment in our securities. Neither the Securities and Exchange Commission nor any state securities commission has approvedordisapproved of these securities or determined if this prospectus supplement and theaccompanying prospectuses is truthful or complete. Any representation to the contrary is a criminaloffense. Delivery of the shares of common stock, common stock warrants and pre-funded warrants is expected tobe made on or about, 2026. The shares of common stock will be settled via the Depository TrustCompany. The common stock warrants and pre-funded warrants will be delivered to purchasers incertificated form. Leerink PartnersBarclays a division of American Capital Partners April, 2026. TABLE OF CONTENTS PROSPECTUS SUPPLEMENT MARKET, INDUSTRY AND OTHER DATA ABOUT THIS PROSPECTUS SUPPLEMENTPROSPECTUS SUPPLEMENT SUMMARYTHE OFFERINGRISK FACTORSSPECIAL STATEMENT REGARDING FORWARD-LOOKING STATEMENTS iiiS-1S-4S-6S-9S- DILUTION DESCRIPTION OF SECURITIES WE ARE OFFERING PROSPECTUS DATED DECEMBER 5, 2025ABOUT THIS PROSPECTUS RISK FACTORSCAUTIONARY STATEMENT REGARDING FORWARD-LOOKING STATEMENTSOUR COMPANYUSE OF PROCEEDSSECURITIES WE MAY OFFERDESCRIPTION OF CAPITAL STOCKDESCRIPTION OF DEBT SECURITIESDESCRIPTION OF WARRANTSDESCRIPTION OF UNITSPLAN OF DISTRIBUTIONLEGAL MATTERSEXPERTSWHERE YOU CAN FIND MORE INFORMATIONINCORPORATION BY REFERENCE PROSPECTUS DATED MARCH 13, 2025ABOUT THIS PROSPECTUS1RISK FACTORS2CAUTIONARY STATEMENT REGARDING FORWARD-LOOKING STAT