Merck to buy Cidara Therapeutics, adding late-stage antiviral drug to its portfolio
Merck (Darmstadt, Germany) will acquire Cidara Therapeutics (CA, USA) in a multibillion-dollar agreement that brings the promising, long-acting influenza antiviral agent CD388 into its pipeline.
Announced on November 14, 2025, the US $9.2 billion deal will give Merck full rights to CD388, Cidara’s Phase 3, long-acting antiviral designed to prevent influenza in people with a high risk of complications. The transaction is expected to close in early 2026 pending regulatory approval and a shareholder tender.
Influenza remains a major global health burden, causing up to 650,000 deaths each year. A preventative option that works across strains, especially for individuals with weaker immune responses, could significantly strengthen public-health defences. This is where CD388 comes in.
An investigational drug-Fc conjugate (DFC), CD388 is designed to deliver season-long, strain-agnostic protection without relying on the immune system. The DFC is comprised of copies of a highly effective small molecule neuraminidase inhibitor that are securely linked to a unique Fc fragment of a human antibody. DFCs are distinct from vaccines and monoclonal antibodies; rather, they are low molecular weight biologics specifically engineered to act as long-lasting small molecule inhibitors.
You may also be interested in:
- Major M&A Deals Impacting Bioanalysis in 2025
- Biopharma’s new blueprint: why partnering and M&A are mission-critical
- Novartis to acquire Avidity Biosciences in $12B deal to boost RNA therapeutics pipeline
The candidate has Breakthrough and Fast Track designations from the US FDA (MD, USA), supported by successful Phase 2b results showing prevention of symptomatic, lab-confirmed influenza, and is now being tested in the 6000-participant ANCHOR Phase 3 trial across the US and UK.
Merck’s leadership said the acquisition complements its respiratory-disease portfolio and positions CD388 as a potential long-term growth driver. Cidara’s CEO described the deal as transformational, enabling the program to benefit from Merck’s global development and commercial capabilities:
“We intend to build on the Cidara team’s remarkable progress and are confident that CD388 has the potential to be another important driver of growth through the next decade, creating real value for shareholders.”
If Phase 3 results are positive, CD388 could offer a new preventive option for high-risk groups as early as later this decade, potentially transforming how seasonal and pandemic influenza are managed worldwide.
