UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

FORM 8-K

CURRENT REPORT

Pursuant to Section 13 or 15(d)

of The Securities Exchange Act of 1934

Date of Report (Date of Earliest Event Reported): June 29, 2021

Altimmune, Inc.

(Exact name of registrant as specified in its charter)

Registrant’s telephone number, including area code: (240) 654-1450

Not Applicable

(Former name or former address, if changed since last report)

Check the appropriate box below if the Form 8-K filing is intended to simultaneously satisfy the filing obligation of the registrant under any of the following provisions:

Securities registered pursuant to Section 12(b) of the Act:

Indicate by check mark whether the registrant is an emerging growth company as defined in Rule 405 of the Securities Act of 1933 (§230.405 of this chapter) or Rule 12b-2 of the Securities Exchange Act of 1934 (§240.12b-2 of this chapter).

Emerging growth company  ¨

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 13(a) of the Exchange Act.  ¨

On June 29, 2021, Altimmune, Inc., or the Company, issued a press release announcing the results of, and an update on, the Phase 1 trial for AdCOVID, the Company’s intranasal COVID-19 vaccine candidate, as well as an update on the Phase 1/2 trial for T-COVID, the Company’s investigational agent for the treatment of early COVID-19.

 A copy of the press release is attached hereto as Exhibit 99.1.

The information in this Item 7.01, including Exhibit 99.1 attached hereto, shall not be deemed “filed” for purposes of Section 18 of the Securities Exchange Act of 1934, as amended, or otherwise subject to the liabilities of that section, nor shall it be deemed incorporated by reference in any filing under the Securities Act of 1933, as amended, except as expressly set forth by specific reference in such a filing.

On June 29, 2021, the Company issued a press release announcing the results of its Phase 1 trial for AdCOVID and the discontinuation of further development of AdCOVID, based in part on the Phase 1 results. The Company also announced that it has terminated further enrollment of its Phase 1/2 trial of T-COVID because of the Company’s inability to enroll subjects in the final cohort as a result of effective rollout in the United States of authorized COVID-19 vaccines and decreasing incidence of disease, which has significantly reduced the number of patients meeting these criteria. The Company is evaluating other development options for the T-COVID program.

(d) Exhibits

SIGNATURES

Pursuant to the requirements of the Securities Exchange Act of 1934, the registrant has duly caused this report to be signed on its behalf by the undersigned hereunto duly authorized.