CD388 (flu prevention, from Cidara)
Acquired from Cidara Therapeutics, completed January 7, 2026; in Phase 3 for influenza prevention.
What it is
Experimental long-acting antiviral for preventing influenza, being studied in a Phase 3 trial in adults and adolescents. Merck bought Cidara for a deal that drove a $9.0B R&D charge in 2026.
Why it matters to the stock. CD388 is Merck's entry into flu prevention. The acquisition charge is large, so the drug has to succeed to justify the 2026 earnings hit.
News
Merck completes $9.2 billion Cidara Therapeutics acquisition for flu-prevention drug CD388
Merck completed its cash tender offer for Cidara Therapeutics at $221.50 per share after about 85.96% of Cidara's shares were tendered by the January 6 expiration, and it moved to a merger to buy the rest.
M&A