Will Weak Gardasil Sales Continue to Weigh on MRK's Top Line in 2026?

Core Insights - Merck (MRK) is experiencing significant challenges with its second-largest product, Gardasil, which saw a 39% year-over-year sales decline to $5.2 billion in 2025 due to sluggish demand, particularly in China and Japan [1][9] Group 1: Gardasil Sales Performance - Gardasil's sales growth was steady through 2022 but began to decline in 2024, with a notable drop in 2025 [1] - The decline in sales is attributed to weak performance in China, where demand trends have been sluggish amid an economic slowdown, leading to high inventory levels at Merck's partner Zhifei [2] - Merck has temporarily halted shipments of Gardasil in China to allow for inventory reduction, and lower demand is also expected to persist in Japan [2][3] Group 2: Other Vaccines and Competition - Besides Gardasil, Merck markets several other vaccines, including ProQuad, M-M-R II, Varivax, Vaxneuvance, RotaTeq, and Pneumovax 23, with many of these also experiencing sales declines in 2025 [4][9] - In contrast, sales of the new vaccine Capvaxive are rising due to increased demand [5] - Merck's new RSV antibody, Enflonsia, recorded $21 million in sales in Q4 2025, down from $79 million in Q3 2025, affected by low immunization rates and high inventory levels [6] Group 3: Competitive Landscape - Enflonsia faces competition from AstraZeneca/Sanofi's RSV antibody Beyfortus, which achieved €1.8 billion in sales in 2025, reflecting a 9.5% year-over-year increase [7] - Other RSV vaccines have also been approved in the U.S., including Pfizer's Abrysvo, GSK's Arexvy, and Moderna's mRESVIA [7] Group 4: Financial Performance and Valuation - Year-to-date, Merck's shares have increased by 10%, outperforming the industry average of 0.8% [8] - Merck's shares are trading at a premium with a price/earnings ratio of 18.40, higher than the industry average of 17.89 and its 5-year mean of 12.57 [10] - The Zacks Consensus Estimate for 2026 earnings per share has decreased from $5.99 to $5.47, and for 2027 from $10.01 to $9.89 over the past 30 days [11]