Merck agreed to acquire Cidara Therapeutics for $9.2 billion, paying $221.50 per share in cash. The deal expands Merck antiviral portfolio ahead of Keytruda 2028 patent expiration and follows its $10 billion Verona Pharma acquisition. Merck will gain CD388, a late-stage therapy aimed at preventing influenza in high-risk individuals. The transaction is expected to close in early 2026.