Merck & Co. Inc. / Cidara Therapeutics, Inc.

Influenza Prevention (High-Risk Populations)

35M US cases/yr · $8.5B Global influenza therapeutics + vaccines market 2024 · 12,000-52,000 Annual US influenza deaths (range)

Disease Overview

Seasonal influenza is an acute respiratory illness caused by influenza A and B viruses that imposes substantial morbidity and mortality, particularly in adults aged 65+, immunocompromised patients (including transplant and hematologic malignancy populations), pregnant women and those with chronic cardiopulmonary or metabolic disease. CDC estimates 9-41 million US symptomatic cases per year, 140,000-710,000 hospitalizations and 12,000-52,000 deaths depending on season severity and strain composition. Annual egg- or cell-based inactivated and recombinant vaccines remain the foundation of prevention, with recombinant and high-dose formulations preferred in older adults, yet seasonal effectiveness ranges widely (10-60%) due to antigenic drift, strain mismatch and immunosenescence. Post-exposure and chemoprophylaxis options are limited to neuraminidase inhibitors (oseltamivir, zanamivir, peramivir) and the cap-dependent endonuclease inhibitor baloxavir, with efficacy dependent on narrow dosing windows and rising baloxavir resistance (PA/I38 mutations). A durable single-dose pre-exposure prophylactic covering an entire influenza season and independent of strain composition would address a long-standing unmet need, particularly for populations in whom vaccines underperform or are contraindicated.

Competitive Landscape

Influenza prevention is anchored by seasonal vaccines. Quadrivalent inactivated vaccines include Fluzone (Sanofi), Fluarix/FluLaval (GSK) and Afluria (Seqirus/CSL); recombinant Flublok (Sanofi) is preferred in 65+; high-dose Fluzone HD (Sanofi) and adjuvanted Fluad (Seqirus) also target elderly populations; the cell-based Flucelvax (Seqirus) and live-attenuated FluMist (AstraZeneca) round out the market. Treatment-class antivirals include oseltamivir (Tamiflu, Roche/Genentech generics, neuraminidase inhibitor), zanamivir (Relenza, GSK), peramivir (Rapivab, BioCryst) and baloxavir marboxil (Xofluza, Shionogi/Roche, cap-dependent endonuclease inhibitor, also approved for post-exposure prophylaxis). mRNA-based seasonal and pandemic flu vaccines are advancing (Moderna mRNA-1010 Phase 3 readout expected 2025; Pfizer mRNA Phase 3 suspended 2024). CD388 (Cidara/Merck) is a first-in-class long-acting drug-Fc conjugate designed as single-dose, universal, strain-agnostic pre-exposure prophylaxis covering a full influenza season, leveraging a neuraminidase inhibitor payload fused to a human IgG1 Fc for ~60-90 day half-life. FDA granted Breakthrough Therapy designation (October 2025) and Fast Track; Phase 3 ANCHOR interim readout is expected Q1 2026. Differentiated positioning targets transplant, oncology and elderly populations where vaccines perform poorly.