MSD eyes 2025/26 RSV vaccine launch after Phase II/III success

MSD (Merck & Co) is working towards the approval and launch of its respiratory syncytial virus (RSV) vaccine, clesrovimab, aiming for availability before the RSV season of 2025-26. This announcement follows the positive outcomes from their Phase IIb/III clinical trial.

In July, MSD first reported that the Phase IIb/III MK-1654-004 trial (NCT04767373), which assessed the efficacy of clesrovimab as a preventive treatment for RSV in infants, achieved its primary objective. The results were further elaborated upon at IDWeek 2024, held from October 16-19 in Los Angeles. The data indicated that clesrovimab reduced the occurrence of RSV-associated medically attended lower respiratory infections requiring at least one indicator by 60% within the first five months post-dosing, compared to a placebo.

MSD is currently in discussions with health authorities worldwide, with the aim of making clesrovimab available for infants in time for the 2025-26 RSV season. If approved, clesrovimab will be positioning itself against AstraZeneca and Sanofi’s Beyfortus (nirsevimab), which is already approved in the United States for preventing RSV lower respiratory tract disease in newborns and infants. Market analysis by GlobalData suggests that Beyfortus, having the first-to-market advantage, is expected to surpass clesrovimab in sales, projecting $2.5 billion in revenue by 2030 compared to $408 million for clesrovimab.

Clesrovimab is characterized as a single-dose, extended half-life monoclonal antibody developed for passive immunization to prevent RSV. The placebo-controlled Phase IIb/III MK-1654-004 trial included 3,632 infants under one year old. Besides meeting its primary endpoint, clesrovimab achieved its secondary endpoint by reducing RSV-associated hospitalizations over five months by 84.2% compared to the placebo. Additionally, the tertiary endpoint—reduction of RSV-associated lower respiratory tract disease hospitalizations by 90.9% compared to placebo over the same period—was also met.

Further data was shared from an interim analysis of the Phase III MK-1654-007 trial (NCT04938830), which compared clesrovimab with Sobi’s RSV monoclonal antibody vaccine, Synagis (palivizumab). This study focused on infants and children at heightened risk for severe RSV illness. At the time of the interim analysis, 901 participants were enrolled. The findings revealed that the safety profile of clesrovimab was comparable to Synagis. The incidence of RSV-associated medically attended lower respiratory infections and hospitalizations was also similar between the two groups, showing 3.6% and 1.3% for clesrovimab, and 3% and 1.5% for Synagis, respectively.

MSD’s pursuit of regulatory approval and the anticipated launch of clesrovimab is poised to offer a significant advancement in the prevention of RSV in infants. This new therapy, if approved, could provide a critical option for protecting young children from the severe impacts of RSV, complementing existing treatments and contributing to broader public health efforts.