Theriva Biologics Inc

Report of Independent Registered Public Accounting Firm

Shareholders and Board of Directors

Theriva Biologics, Inc.

Rockville, Maryland

Opinion on the Consolidated Financial Statements

We have audited the accompanying consolidated balance sheets of Theriva Biologics, Inc. (the “Company”) as of December 31, 2023 and 2022, the related consolidated statements of operations and comprehensive income, stockholders’ equity, and cash flows for each of the years then ended, and the related notes (collectively referred to as the “consolidated financial statements”). In our opinion, the consolidated financial statements present fairly, in all material respects, the financial position of the Company at December 31, 2023 and 2022, and the results of its operations and its cash flows for the years then ended, in conformity with accounting principles generally accepted in the United States of America.

Going Concern Uncertainty

The accompanying consolidated financial statements have been prepared assuming that the Company will continue as a going concern. As discussed in Note 2 to the consolidated financial statements, the Company has suffered recurring losses from operations and has not generated positive cash flows from operations which raise substantial doubt about its ability to continue as a going concern. Management’s plans in regard to these matters are also described in Note 2. The consolidated financial statements do not include any adjustments that might result from the outcome of this uncertainty.

Basis for Opinion

These consolidated financial statements are the responsibility of the Company’s management. Our responsibility is to express an opinion on the Company’s consolidated financial statements based on our audits. We are a public accounting firm registered with the Public Company Accounting Oversight Board (United States) (“PCAOB”) and are required to be independent with respect to the Company in accordance with the U.S. federal securities laws and the applicable rules and regulations of the Securities and Exchange Commission and the PCAOB.

We conducted our audits in accordance with the standards of the PCAOB. Those standards require that we plan and perform the audit to obtain reasonable assurance about whether the consolidated financial statements are free of material misstatement, whether due to error or fraud. The Company is not required to have, nor were we engaged to perform, an audit of its internal control over financial reporting. As part of our audits, we are required to obtain an understanding of internal control over financial reporting but not for the purpose of expressing an opinion on the effectiveness of the Company’s internal control over financial reporting. Accordingly, we express no such opinion.

Our audits included performing procedures to assess the risks of material misstatement of the consolidated financial statements, whether due to error or fraud, and performing procedures that respond to those risks. Such procedures included examining, on a test basis, evidence regarding the amounts and disclosures in the consolidated financial statements. Our audits also included evaluating the accounting principles used and significant estimates made by management, as well as evaluating the overall presentation of the consolidated financial statements. We believe that our audits provide a reasonable basis for our opinion.

Critical Audit Matters

The critical audit matters communicated below are matters arising from the current period audit of the consolidated financial statements that were communicated or required to be communicated to the audit committee and that: (1) relate to accounts or disclosures that are material to the consolidated financial statements and (2) involved our especially challenging, subjective, or complex judgments. The communication of critical audit matters does not alter in any way our opinion on the consolidated financial statements, taken as a whole, and we are not, by communicating the critical audit matters below, providing separate opinions on the critical audit matters or on the accounts or disclosures to which they relate.

Contingent Consideration – Fair value measurement

As discussed in Notes 3 and 5 to the consolidated financial statements, during 2022 the Company completed the acquisition of VCN Biosciences (“VCN”). The purchase consideration transferred included contingent consideration of up to $70.25 million based on the

achievement of certain clinical and commercialization milestones of an acquired product, VCN-01, and was initially recorded at its estimated fair value as of the date of acquisition. Subsequent to the date of acquisition, the Company reassesses the fair value at each balance sheet date and the contingent consideration liability was recorded at an estimated fair value of $6.3 million as of December 31, 2023 utilizing the discounted cash flow method.

We identified the determination of the fair value of the contingent consideration liability as a critical audit matter. Under the discounted cash flow method, the key estimates and assumptions used in the valuation of the contingent consideration liability included management’s determination of the probability weighted estimates of future earn-out payments based on successful achievement of certain clinical and commercialization milestones, and the estimated discount rate applicable to the future payment periods. Changes to these key estimates and assumptions could have a significant impact on the fair value of the contingent consideration liability. Auditing management’s valuation methods and these assumptions involve especially challenging and subjective auditor judgment due to the nature and extent of auditor effort required to address these matters, including the specialized knowledge and skill needed.

The primary procedures we performed to address this critical audit matter included:

In-Process Research and Development and Goodwill Impairment Assessment

As described in Notes 3 and 6 to the consolidated financial statements, the Company’s consolidated balances of In-process Research and Development (“IPR&D”) indefinite-lived intangible asset and Goodwill were $19.8 million and $5.7 million, respectively, as of December 31, 3023. The Company reviews goodwill for impairment at least annually and or more frequently if events or circumstances indicate the carrying value at the reporting unit level might exceed its fair value. The IPR&D indefinite-lived intangibles are tested annually for impairment, or more frequently if events or circumstances indicate it is more likely than not the fair value is less than their carrying value. The Company estimates the fair value of its reporting unit and certain IPR&D using an income approach. The Company identified a triggering event during 2023 and performed an impairment analysis for Goodwill and certain IPR&D resulting in no impairment charges being recorded.

We identified the determination of the fair value of the Company’s reporting unit and certain IPR&D as a critical audit matter. Under the income approach, the key assumptions used in the determination of the fair value of the reporting unit include estimates of future cash flows, the discount rate applicable to those future cash flow periods, and the implied control premium. The key assumptions used in the determination of the fair value of certain IPR&D assets using the income approach include estimates of future cash flows and the discount rate applicable to those future cash flow periods. Changes to these key assumptions could have a significant impact on the measurement of the fair value of the reporting unit and certain IPR&D. Auditing management’s valuation methods and these assumptions involve especially challenging and subjective auditor judgment due to the nature and extent of auditor effort required to address these matters, including the specialized knowledge and skill needed.

The primary procedures we performed to address this critical audit matter included:

/s/BDO USA, P.C.

Raleigh, North Carolina

March 25, 2024

We have served as the Company's auditor since 2012.