Altimmune, Inc.

NOTES TO CONSOLIDATED FINANCIAL STATEMENTS

(Unaudited)

1. Nature of Business and Basis of Presentation

Nature of Business

Altimmune, Inc., headquartered in Gaithersburg, Maryland, United States, together with its subsidiaries (collectively, the “Company” or “Altimmune”) is a late clinical-stage biopharmaceutical company incorporated under the laws of the State of Delaware.

The Company is developing novel therapies for serious liver diseases. The Company’s lead product candidate is pemvidutide (formerly known as ALT-801), a balanced 1:1 glucagon/GLP-1 dual receptor agonist in development for the treatment of metabolic dysfunction-associated steatohepatitis (“MASH”), alcohol use disorder (“AUD”) and alcohol-associated liver disease (“ALD”). The Company may also pursue additional indications for pemvidutide that leverage its differentiated clinical profile. Since its inception, the Company has devoted substantially all of its efforts to business strategy and planning, research and development, recruiting management and technical staff, and raising capital, and has financed its operations through the issuance of common and preferred stock, long-term debt, and proceeds from research grants and government contracts. The Company has not generated any revenues from the sale of any products to date, and there is no assurance of any future revenues from product sales.

Basis of Presentation

The accompanying unaudited consolidated financial statements are prepared pursuant to the rules and regulations of the U.S. Securities and Exchange Commission (“SEC”) regarding interim financial reporting. Accordingly, they do not include all of the information and disclosures required by accounting principles generally accepted in the United States (“U.S. GAAP”) for complete consolidated financial statements and should be read in conjunction with the audited consolidated financial statements for the year ended December 31, 2025, included in the Annual Report on Form 10-K, which was filed with the SEC on March 6, 2026. In the opinion of management, the Company has prepared the accompanying unaudited consolidated financial statements on the same basis as the audited consolidated financial statements, and these consolidated financial statements include all adjustments, consisting only of normal recurring adjustments, necessary for a fair presentation of the results of the interim periods presented. The operating results for the interim periods presented are not necessarily indicative of the results expected for the full year 2026 or any future years or periods.

The accompanying unaudited consolidated financial statements include the accounts of the Company and its wholly owned subsidiaries. All significant intercompany accounts and transactions have been eliminated in consolidation.

The accompanying unaudited consolidated financial statements have been prepared on the basis of continuity of operations, realization of assets, and the satisfaction of liabilities in the ordinary course of business. The financial statements do not include any adjustments relating to the recoverability and classification of recorded assets and liabilities that might be necessary should the Company be unable to continue as a going concern.

2. Summary of Significant Accounting Policies

During the three months ended March 31, 2026, there have been no significant changes to the Company’s summary of significant accounting policies contained in the Company’s Annual Report on Form 10-K for the year ended December 31, 2025, as filed with the SEC on March 6, 2026.

Use of Estimates

The preparation of financial statements in conformity with U.S. GAAP requires management to make estimates and assumptions that affect the amounts reported in the financial statements and accompanying notes. Significant estimates and assumptions made in the accompanying condensed consolidated financial statements include, but are not limited to, the valuation of share-based awards, income taxes, prepaids, and accruals for research and development activities. The Company bases its estimates on historical experience and on various other assumptions that are believed to be reasonable. However, actual results could differ from those estimates.

Impairment or Disposal of Long-lived Assets

Long-lived assets are reviewed for impairment whenever events or changes in circumstances indicate the carrying value of such assets may not be recoverable in accordance with the guidance in Financial Accounting Standards Board (“FASB”) Accounting Standard Codification Topic 360,Property, Plant and Equipment (“ASC 360”). The Company’s long-lived assets include properties and equipment and right of use (“ROU”) assets. For long-lived assets, impairment is recognized when the undiscounted cash flows used in the test for recoverability is less than their carrying value, and the fair value of the long-lived asset is below the carrying value. In the event impairment exists, the long-lived asset will be written down to its fair value, and an impairment loss is recorded as the difference between the carrying value and fair value. During the three months ended March 31, 2026, the Company recognized an impairment charge of $0.7 million related to its office and laboratory lease ROU asset and underlying leasehold improvements and equipment. The Company determined the fair value of each asset group using a discounted cash flow model based on the expected sublease income utilizing its current borrowing rate. The inputs utilized for fair value measurement are unobservable and considered level 3 in the fair value hierarchy. The impairment charge was recorded in “Research and development expense” in the Consolidated Statement of Operations and Comprehensive Loss, and reduced the carrying amount of the underlying long-lived assets to fair value.

3. Fair Value Measurements

The Company’s assets measured at fair value on a recurring basis as of March 31, 2026, consisted of the following (in thousands):

The Company’s assets measured at fair value on a recurring basis as of December 31, 2025, consisted of the following (in thousands):

Short-term investments have been initially valued at the transaction price and subsequently valued at the end of each reporting period utilizing third party pricing services or other market observable data (Level 2). The pricing services utilize industry standard valuation models, including both income and market-based approaches and observable market inputs to determine value. The Company’s short-term investments have a maturity date of one year or less.

Short-term investments with quoted prices as of March 31, 2026, as shown below (in thousands):

Short-term investments with quoted prices as of December 31, 2025, as shown below (in thousands):

As of March 31, 2026 and December 31, 2025, none of the unrealized losses on the Company’s short-term investments are a result of credit loss, therefore, any unrealized losses were recognized in other comprehensive income (OCI).

As of March 31, 2026 and December 31, 2025, the Company had $1.4 million and $1.1 million, respectively, accrued interest on short-term investments included in “Accounts and other receivables” on the accompanying Consolidated Balance Sheets.

The carrying amounts of the Company’s debt approximate fair value because the rates are floating rates based on the prime lending rate, which approximates market rates (see Note 5) and represents a Level 2 fair value measurement.

Separate disclosure is required for assets and liabilities measured at fair value on a recurring basis from those measured at fair value on a non-recurring basis. Assets recorded at fair value on a non-recurring basis, such as property and equipment and intangible assets are recognized at fair value when they are impaired. As of March 31, 2026 and December 31, 2025, the Company hadno other assets or liabilities that were measured at fair value on a non-recurring basis.

4. Accrued Expenses

Accrued expenses and other current liabilities consist of the following (in thousands):

5. Term Loan

On May 13, 2025 (“Closing Date”), the Company and certain of its subsidiaries entered into a Loan and Security Agreement (“Loan Agreement”) with Hercules Capital, Inc. (“Hercules”) and the lenders party thereto, pursuant to which the lenders will make available up tofour tranches of term loans in an aggregate principal amount of $100.0 million (the “Term Loan”), subject to certain terms and conditions. Under the terms of the Loan Agreement, the first Term Loan tranche was drawn down on the Closing Date in an aggregate principal amount of $15.0 million. Upon the achievement of certain milestones and subject to other terms and conditions set out in the Loan Agreement, (i) the second Term Loan tranche was to be made available in an aggregate principal amount of up to $25.0 million and (ii) the third Term Loan tranche was to be made available in an aggregate principal amount of up to $15.0 million. The fourth Term Loan tranche was to be made available in an aggregate principal amount of up to $45.0 million subject to the approval of the lenders. The Term Loan had interest rate equal to the greater of (a) theprime rate as reported in The Wall Street Journal plus 2.45% and (b) (i)9.95% until December 31, 2025, and (ii)9.45% thereafter.

On November 5, 2025, (the “Amendment Closing”), the Company entered into an amendment to the Loan Agreement with Hercules and the lenders party thereto, pursuant to which the lenders will, subject to certain terms and conditions, increase the availability under the Term Loan from an aggregate principal amount of $100.0 million to $125.0 million. The Term Loan, as amended, is structured infour tranches. As described above, the first Term Loan tranche was drawn down on the Closing Date in an aggregate principal amount of $15.0 million. The second Term Loan tranche was drawn down on the Amendment Closing in an aggregate principal amount of $20.0 million. Upon the achievement of certain milestones and subject to other terms and conditions set out in the Loan Agreement, as amended, the third Term Loan tranche will be made available in an aggregate principal amount of up to $10.0 million. The fourth Term Loan tranche will be made available in an aggregate principal amount of up to $80.0 million subject to the approval of the lenders. The Term Loan, as amended, bears interest equal to the greater of (a)9.70% per annum and (b) theprime rate as reported in The Wall Street Journal plus 2.45% per annum. The interest-only period has been extended to 30 months from May 13, 2025.

The Term Loan will mature on January 1, 2029 (the “Maturity Date”). The Company may make payments of interest only through December 1, 2027, which will be extended to June 1, 2028, or December 1, 2028, if certain conditions described in the Loan Agreement, as amended, are met. Thereafter, the Company is obligated to make payments that will include installments of principal and interest through the Maturity Date.

The Loan Agreement includes customary representations and warranties and covenants associated with the Term Loan. Such terms include (1) covenants concerning financial and other reporting obligations, and (2) certain limitations on indebtedness, liens, investments, distributions (including dividends), collateral, transfers, mergers or acquisitions, taxes, corporate changes, and deposit accounts. Compliance with the financial covenant will be conditionally waived pursuant to the terms of the Loan Agreement when the Company’s market capitalization exceeds $800 million. The Loan Agreement includes customary events of default, including payment defaults, breaches of representations and warranties, breaches of covenants following any applicable cure period and the occurrence of certain events that could reasonably be expected to have a “material adverse effect” as set forth in the Loan Agreement. As of March 31, 2026, the Company was in compliance with the covenants under the Loan Agreement.

The obligation under the Loan Agreement is secured by a security interest in substantially all of the Company’s assets and the assets of its subsidiaries that are co-borrowers or guarantors. Upon the occurrence of an event of default, Hercules will be entitled to exercise remedies, including acceleration of the Term Loan obligations and foreclosure on collateral.

The Loan Agreement, as amended, provides for a prepayment charge equal to 3.0% of the outstanding principal balance of the Term Loan if prepayment is made within thetwelve months after Amendment Closing,2.0% if within thetwenty-four months after Amendment Closing,1.0% if within thethirty-six months after Amendment Closing and 0.0% thereafter. The Loan Agreement provides for an end of term charge of 6.25% of the funded loan amount, due at the earlier of prepayment or maturity. Pro-rata payment of any earned end of term charge will be due upon any partial prepayment (the “End of Term Charge”). In addition, the Loan Agreement requires the Company to pay a facility charge of 1.0% of

the Term Loan funded due at the Closing Date and of each subsequent Term Loan tranche at the time such tranche is funded.

The Company accounted for the End of Term Charge, Facility Charge, and other direct costs incurred in connection with the Loan Agreement and its amendment as a debt discount and issuance costs, and they are being amortized over the term of the loan using the effective interest method. The weighted-average effective interest rate on the Term Loan is 13.37%.

The Company incurred interest expense on the Term Loan, including debt discount and issuance costs amortization, of $1.1 million during the three months ended March 31, 2026.

The Term Loan consists of the following (in thousands):

Future principal loan payments on the currently outstanding Term Loan as of March 31, 2026 are as follows (in thousands):

6. Other Noncurrent Liabilities

The Company’s other noncurrent liabilities are summarized as follows (in thousands):

7. Stockholders’ Equity

The Amended and Restated Certificate of Incorporation, as amended (“Charter”), authorized the Company to issue 200,000,000 shares of common stock, par value $0.0001 per share. As of March 31, 2026, the Company had 130,221,154 shares of common stock issued andoutstanding.

Each share of common stock entitles the holder toone vote on all matters submitted to a vote of the Company’s stockholders. Common stockholders are not entitled to receive dividends, unless declared by the board of directors.

The Charter also authorized the Company to issue 1,000,000 shares of preferred stock, par value $0.0001 per share. As of March 31, 2026, the Company hadno shares of preferred stock issued andoutstanding.

At-the-Market (ATM) Offerings

On November 6, 2025, the Company entered into an Equity Distribution Agreement (the “November 2025 Agreement”) with Leerink Partners LLC serving as sales agent (the “November 2025 Sales Agent”) with respect to an ATM offerings program under which the Company may offer and sell, from time to time at its sole discretion, shares of its common stock, having an aggregate offering price of up to $200.0 million (the “November 2025 Shares”) through the November 2025 Sales Agent (the “November 2025 Offering”). All Shares offered and sold in the November 2025 Offering will be issued pursuant to the Company’s Registration Statement on Form S-3 filed with the SEC on February 27, 2025, which was declared effective on March 13, 2025, and the prospectus supplements related to the November 2025 Offering that form a part of the Registration Statement. The Company capitalized approximately $0.2 million of other offering costs which will offset the proceeds received from the shares sold under the November 2025 Agreement. Since inception through March 31, 2026, the Company has sold 7,920,228 shares of common stock under the November 2025 Agreement resulting in approximately $34.2 million in proceeds, net of $0.6 million commission and other offering costs. During the three months ended March 31, 2026, the Company sold 2,021,169 shares of common stock under the November 2025 Agreement resulting in approximately $8.7 million in proceeds, net of $0.1 million commission and other offering costs, and as of March 31, 2026, $165.3 million remained available to be sold under the November 2025 Agreement. As of March 31, 2026, there was $0.2 million deferred offering costs included in prepaid expenses and other current assets on the accompanying consolidated balance sheets.

On February 27, 2025, the Company entered into an Equity Distribution Agreement (the “February 2025 Agreement”) with Leerink Partners LLC, Piper Sandler & Co. and Stifel, Nicolaus & Company, Incorporated, serving as sales agents (the “February 2025 Sales Agents”) with respect to an ATM offerings program under which the Company offered and sold shares of its common stock, having an aggregate offering price of up to $150.0 million (the “February 2025 Shares”) through the February 2025 Sales Agents (the “February 2025 Offering”). All Shares offered and sold in the 2025 Offering were issued pursuant to the Company’s Registration Statement on Form S-3 filed with the SEC on February 27, 2025, which was declared effective on March 13, 2025, and the prospectus supplements related to the February 2025 Offering that form a part of the Registration Statement. During the three months ended March 31, 2025, the Company sold 805,502 shares of common stock under the February 2025 Agreement for net proceeds of approximately $4.6 million. Since inception through the termination of the February 2025 Agreement in November 2025, the Company sold 27,896,642 shares of common stock resulting in approximately $118.1 million in proceeds, net $3.9 million commission and other offering costs.

On February 28, 2023, the Company entered into an Equity Distribution Agreement (the “2023 Agreement”) with Evercore Group L.L.C., JMP Securities LLC and B. Riley Securities, Inc., serving as sales agents (the “2023 Sales Agents”), with respect to an ATM offerings program under which the Company offered and sold shares of its common stock, having an aggregate offering price of up to $150.0 million (the “2023 Shares”) through the 2023 Sales Agents (the “2023 Offering”). All 2023 Shares offered and sold in the 2023 Offering were issued pursuant to the Company’s Registration Statement on Form S-3 filed with the SEC on February 28, 2023. During the three months ended March 31, 2025, the Company sold 4,467,866 shares of common stock under the 2023 Agreement for net proceeds of approximately $30.2 million. Since inception through the termination of the 2023 Agreement in February 2025, the Company sold 26,129,903 shares of common stock under the 2023 Agreement resulting in approximately $126.8 million in proceeds, net of $4.1 million commission and other offering costs.

Registered Direct Offering (“RDO”)

On January 27, 2026, the Company entered into a securities purchase agreement with a new fundamental institutional investor pursuant to a registered direct offering under the November 2025 Shelf for the purchase and sale of 12,397,920 shares of its common stock and 4,647,534 pre-funded warrants for net proceeds of approximately $70.3 million (the “January 2026 RDO”). All Shares offered and sold in the January 2026 RDO were issued pursuant to the Company’s Registration Statement on Form S-3 filed with the SEC on November 13, 2025, which was declared effective on December 5, 2025. The pre-funded warrants were fully exercised on February 13, 2026 at an exercise price of $0.001 per share, resulting in the issuance of 4,647,534 shares of the Company’s common stock.

The pre-funded warrants are indexed to the Company’s common stock and meet the criteria to be classified as equity. Proceeds from the issuance of pre-funded warrants are recorded within additional paid-in capital.

8. Stock-Based Compensation

2017 Omnibus Incentive Plan (Omnibus Plan)

The Company’s Omnibus Plan provides for an annual increase on January 1 of each year commencing in 2019 and ending on and including January 1, 2027, up to an amount equal to the lowest of (i)4% of the total number of shares of common stock outstanding on a fully diluted basis as of December 31 of the immediately preceding calendar year, and (ii) such number of shares of common stock, if any, determined by the Company’s board of directors. Accordingly, on January 1, 2026, the number of shares of Common Stock reserved and available for issuance under the Omnibus Plan increased by 4,969,458 shares of common stock.

Stock Options

The Company’s stock option awards generally vest over four years and typically have a contractual life often years. As of March 31, 2026, there was $20.6 million of unrecognized compensation cost related to stock options, which is expected to be recognized over a weighted-average period of 3.2 years. During the three months ended March 31, 2026, the Company granted 1,607,663 stock options with a weighted average exercise price of $4.52 and per share weighted average grant date fair value of $3.75.

Information related to stock options outstanding as of March 31, 2026, is as follows (in thousands, except share, exercise price, and contractual term):

Restricted Stock Units (RSUs)

During the three months ended March 31, 2026, the Company granted 672,517 shares of RSUs with a weighted average grant date fair value of $4.52 which vest over four years. As of March 31, 2026, the Company had unvested RSUs of 2,159,982 shares with total unrecognized compensation expense of $7.9 million, which the Company expects to recognize over a weighted average period of approximately 3.4 years. During the three months ended March 31, 2026, the

Company issued 209,537 shares common stock as a result of the vesting of 333,575 RSUs, net of 124,038 shares of common stock withheld to satisfy tax withholding obligations.

2019 Employee Stock Purchase Plan (“ESPP”)

Under the ESPP, employees purchased 57,801 shares for $0.2 million during the three months ended March 31, 2026.

Stock-based Compensation Expense

During the three months ended March 31, 2026, the Company recorded $0.3 million in incremental stock-based compensation expense as a result of the modifications of stock awards upon termination of a former executive officer. The modification extended the option exercise period of a former executive officer’s fully vested stock options by a period of twelve months from the termination date.

Stock-based compensation expense is classified in the unaudited consolidated statements of operations and comprehensive loss for the three months ended March 31, 2026 and 2025 as follows (in thousands):

9. Net Loss Per Share

Because the Company has reported net loss attributable to common stockholders for the three months ended March 31, 2026 and 2025, basic and diluted net loss per share attributable to common stockholders in each period are the same.

Basic net loss per share attributable to common stockholders is computed by dividing the net loss attributable to common stockholders by the weighted average numbers of shares of common stock and pre-funded warrant outstanding for the period.

Diluted net loss per share is calculated by adjusting weighted average shares outstanding for the dilutive effect of common stock equivalents outstanding for the period. As such, all unvested RSUs and stock options have been excluded from the computation of diluted weighted average shares outstanding because such securities would have an anti-dilutive impact for all periods presented.

Potential common shares issuable upon conversion, vesting, or exercise of unvested RSUs and stock options that are excluded from the computation of diluted weighted-average shares outstanding, as they are anti-dilutive, are as follows:

10. Commitments and Contingencies

Spitfire Acquisition

In July 2019, the Company entered into the Spitfire merger agreement to acquire all of the equity interests of Spitfire Pharma, Inc. (“Spitfire”). Spitfire was a privately held, preclinical pharmaceutical company developing novel

peptide products for pharmaceutical indications, including pemvidutide for the treatment of MASH. As part of the agreement, the Company is obligated to make payments of up to $80.0 million upon the achievement of specified worldwide net sales of all products developed using the technology acquired from Spitfire Pharma, Inc. (the “Sales Milestone”) withinten years following the approval of a new drug application filed with the U.S. Food and Drug Administration (the “FDA”).

The contingent payments related to the Sales Milestones are predominately cash-based payments accounted for under FASB Accounting Standards Codification Topic 450, Contingencies. Accordingly, the Company will recognize the Sales Milestones when the contingency is probable and the amount can be reasonably estimated.

Litigation

The Company from time to time may be a party in various contracts and subject to disputes, litigation, and potential claims arising in the ordinary course of business none of which are currently reasonably possible or probable of material loss.

11. Segment Information

The Company is a late clinical-stage biopharmaceutical company developing novel therapies for serious liver diseases. The Company’s lead product candidate is pemvidutide, a balanced 1:1 glucagon/GLP-1 dual receptor agonist in development for the treatment of MASH, AUD and ALD. To date, the Company has not generated any revenue from the sale of any products.

The chief operating decision maker assesses the performance of the Company and decides how to allocate resources based solely on net (loss) income, which is also reported on the consolidated statements of operations and comprehensive loss as net (loss) income. The measure of segment assets is reported on the consolidated balance sheet as total assets.

12. Subsequent Events

The Company evaluated subsequent events through the issuance date of the financial statements.

On April 16, 2026, the Company amended its Charter by filing a Certificate of Amendment with the Secretary of State of Delaware. The Certificate of Amendment reflected an amendment to increase the number of authorized shares of common stock from 200,000,000 to 400,000,000 and was approved by the holders of more than a majority of the votes cast at the 2026 Annual Meeting of Shareholders. In addition, the Company also amended its ESPP to increase the number of shares of common stock reserved under the ESPP from 403,500 to 1,108,827.

On April 22, 2026, the Company entered into an underwriting agreement with certain underwriters pursuant to which the Company offered and sold securities consisting of (i)64,250,000 shares of its common stock and accompanying common stock warrants to purchase an aggregate of 64,250,000 shares of common stock (or pre-funded warrants in lieu thereof) and (ii) in lieu of common stock, to certain investors that so choose, pre-funded warrants to purchase an aggregate of up to 10,750,000 shares of its common stock and accompanying common stock warrants to purchase an aggregate of 10,750,000 shares of common stock (or pre-funded warrants in lieu thereof), at an exercise price of $0.001 per pre-funded warrant (the “April 2026 Offering”). The common stock and pre-funded warrants were sold in combination with an accompanying common stock warrant to purchaseone share of common stock (orpre-funded warrant in lieu thereof) issued for each share of common stock or pre-funded warrant sold. The accompanying common stock warrant has an exercise price of $3.00 per share and is immediately exercisable from the date of issuance. The combined offering price of each share of common stock and accompany common stock warrant is $3.00. The combined offering price of each pre-funded warrant and accompanying common stock warrant is $2.999. The net proceeds of the April 2026 Offering were approximately $211.2 million, after deducting the underwriting discount and estimated offering expenses. If all of the common stock warrants sold in the April 2026 Offering were to be exercised in cash at their exercise price, the Company would receive additional gross proceeds of $225 million. All shares of common stock, pre-funded warrants and common stock warrants offered and sold in the April 2026 Offering were issued pursuant to the February 2025 Shelf and November

2025 Shelf and a related registration statement that was filed with the SEC on April 22, 2026 pursuant to Rule 462(b) under the Securities Act of 1933, as amended, and became automatically effective upon filing as permitted under Rule 429.