Altimmune, Inc. New Standards Disclosure

Recently issued accounting pronouncements

Recently Adopted:

In December 2023, the FASB issued ASU No. 2023-09, Income Taxes (Topic 740): Improvements to Income Tax Disclosures. ASU No. 2023-09 requires public business entities on an annual basis to (i) disclose in the rate reconciliation both percentages and amounts for certain categories in a tabular format, with further disaggregation of certain categories when the individual reconciling items meet a quantitative threshold, (ii) disclose income taxes paid, net of refunds received disaggregated by federal, state and foreign, with further disaggregation by individual jurisdictions that meet a qualitative threshold (iii) eliminates the requirement to disclose certain information when it is reasonably possible that the total

amounts of unrecognized tax benefits will significantly increase or decrease within 12 months of the reporting date or make a statement that an estimate of the range cannot be made and (iv) eliminates the requirement to disclose cumulative amount of each type of temporary difference in certain circumstances. The amendments in ASU 2023-09 are effective for fiscal years beginning after December 15, 2024, with early adoption permitted for annual financial statements that have not yet been issued. The Company adopted ASU No. 2023-09 on this annual report on Form 10-K using a prospective method (See Note 12. Income Taxes).

Not Yet Adopted:

In December 2025, the FASB issued ASU No. 2025-10, Government Grants – Accounting for Government Grants Received by Business Entities (Topic 832). The amendments in ASU No. 2025-10 establish the accounting for a government grant received by a business entity, including guidance for (1) a grant related to an asset and (2) a grant related to income. A grant related to an asset is a government grant, or part of a government grant, that is conditioned on the purchase, construction, or acquisition of an asset (for example, a long-lived asset or inventory). A grant related to income is a government grant, or part of a government grant, other than a grant related to an asset (for example, a grant that reimburses a business entity for operating expenses). The amendment require that a government grant received by a business entity should not be recognized until (1) It is probable that (a) a business entity will comply with the conditions attached to the grant and (b) the grant will be received and (2) business entity meets the recognition guidance for a grant related to an asset or a grant related to income. The amendments in ASU 2025-10 are effective for annual reporting periods beginning after December 15, 2028. Early adoption is permitted. The Company is currently evaluating the impact of this amendment on its Consolidated Financial Statements.

In November 2024, the FASB issued ASU No. 2024-03, Income Statement – Reporting Comprehensive Income-Expense Disaggregation Disclosure (Subtopic 220-40). The amendments in ASU No. 2024-03 require that, at each interim and annual reporting period, public business entities disclose in a note to the financial statements the amount of (i) purchases of inventory, (ii) employee compensation, (iii) depreciation, (iv) intangible asset amortization, and (v) depreciation, depletion, and amortization recognized as part of oil and gas-producing activities (DD&A) (or other amounts of depletion expense) included in each relevant expense caption in the statements of operation and comprehensive income. The amendments in ASU 2024-03 are effective for annual reporting periods beginning after December 15, 2026, and interim reporting periods within annual reporting periods beginning after December 15, 2027. Early adoption is permitted. The amendments should be applied either prospectively to financial statements issued for reporting periods after the effective date or retrospectively to any or all prior periods presented in the financial statements. The amendments in this update are effective on the Company’s 2027 annual report, and interim reports thereafter. The Company is currently evaluating the impact of this amendment on its Consolidated Financial Statements.