Merck to Acquire Cidara Therapeutics in $9.2 Billion Deal to Bolster Flu Portfolio

Merck & Co. (NYSE: MRK) announced Friday it will acquire Cidara Therapeutics (NASDAQ: CDTX) in a $9.2 billion all-cash transaction, marking its latest move to expand in infectious disease and diversify ahead of the expected patent expiration of its blockbuster cancer therapy, Keytruda, later this decade.Under the agreement, Merck will pay $221.50 per Cidara share, representing a 108.9% premium over Cidara’s last closing price. Shares of Cidara surged to $217.89, while Merck slipped 1.3% following the announcement.

The San Diego–based biotech’s lead asset, CD388, is an experimental long-acting antiviral designed to prevent influenza across multiple strains and immune profiles. Unlike a traditional vaccine, CD388 is a drug-Fc conjugate combining zanamivir…the active component in GSK’s influenza drug Relenza…with a validated human antibody fragment. The drug aims to provide season-long protection from a single dose and is currently being evaluated in a late-stage trial involving adults and adolescents at high risk for flu complications. 

“We are confident that CD388 has the potential to be another important driver of growth through the next decade,” said Merck CEO Robert Davis in a statement. The acquisition follows a string of major deals as Merck broadens its late-stage pipeline to reduce reliance on Keytruda, which generated more than $25 billion in annual sales.

Since 2021, Merck has nearly tripled its late-stage pipeline, highlighted by the $11.5 billion Acceleron purchase for pulmonary hypertension drug Winrevair and the $10 billion acquisition of Verona Pharma in July, adding Ohtuvayre for chronic obstructive pulmonary disease. “There definitely seems to be a sense of urgency at Merck to add growth to their pipeline via deals,” said James Harlow, senior vice president at Novare Capital Management.

CD388 has demonstrated encouraging mid-stage results. In a Phase 2 trial, the antiviral provided up to 76% protection from symptomatic influenza over 24 weeks versus placebo in unvaccinated adults aged 18 to 64. 

The therapy has received Breakthrough Therapy Designation from the U.S. Food and Drug Administration, allowing for an accelerated review.Cidara expects to complete enrollment of 6,000 participants in its pivotal Phase 3 trial by December 2025.Analysts see the acquisition as both a diversification play and a calculated risk. “While this deal is somewhat complementary, it is not perfectly ‘plug and play’ with the rest of the Merck portfolio,” said Bernstein analyst Courtney Breen, describing Cidara as “essentially a single-asset story.”

Still, Breen said the deal provides late-decade, lower-risk revenue, with potential long-term payoff as Merck builds a presence in respiratory antivirals.Through a subsidiary, Merck will acquire all outstanding shares of Cidara in a transaction valued at approximately $6.96 billion in equity, with milestone and transaction costs bringing the total to about $9.2 billion. The deal is expected to close in the first quarter of 2026, subject to customary regulatory approvals.

About Merck & Co., Inc.

Merck & Co., Inc. (NYSE: MRK), known as MSD outside the United States and Canada, is a global biopharmaceutical company headquartered in Rahway, New Jersey. Founded in 1891, Merck develops prescription medicines, vaccines, biologic therapies, and animal health products. The company’s mission is to deliver innovative health solutions that advance the prevention and treatment of diseases worldwide.

About Cidara Therapeutics, Inc.

Cidara Therapeutics, Inc. (NASDAQ: CDTX) is a clinical-stage biotechnology company based in San Diego, California, developing long-acting therapeutics designed to improve the standard of care for serious diseases. Its lead candidate, CD388, is an antiviral for universal influenza prevention and treatment, currently in Phase 3 development.

At the time of publishing, Stocks.News holds position in Merck & Co. as mentioned in the article.