Three months after revealing that its respiratory syncytial virus (RSV) preventive antibody clesrovimab had passed muster in a phase 2b/3 trial, Merck is putting numbers to the claim.
Clesrovimab, also known as MK-1654, scored on multiple trial endpoints, demonstrating its ability to protect infants against the virus in their first RSV season.
With the results, which were presented Thursday in Los Angeles during IDWeek 2024, Merck said it hopes to bring clesrovimab to the market for the 2025-26 RSV season.
Clesrovimab achieved its primary objective by reducing the incidence of RSV-associated medically attended lower respiratory infections requiring at least one indicator of lower respiratory infection by 60% versus placebo through the first five months after dosing, the company said.
The drug also reduced RSV-related hospitalizations (secondary endpoint) and RSV-related lower respiratory infection hospitalizations (tertiary endpoint) by 84% and 91%, respectively, versus placebo through five months.
“The (study) evaluated a broad spectrum of RSV disease ranging from mild outpatient illness to severe disease requiring hospitalization,” Octavio Ramilo, M.D., trial investigator and chairman of the department of infectious diseases at St. Jude’s Children’s Research Hospital, said in a release. “These promising results demonstrating decreased incidence of RSV disease, including hospitalizations, highlight the potential for clesrovimab to play an important role in helping to alleviate the continued burden of RSV on infants and their families.”
Merck also provided interim results of a phase 3 trial of clesrovimab going head-to-head against Synagis (palivizumab) in infants at increased risk for severe RSV. The trial achieved its primary goal, showing comparable safety and tolerability to the vaccine, which was approved in 1998 for at-risk babies.
Merck once had an RSV candidate for adults in early-stage development but passed it over to longtime partner Moderna in 2020 to focus on what would become clesrovimab. For its part, Moderna has powered ahead in the RSV space, scoring FDA approval for an adult RSV vaccine in May.
In the RSV market for infants, AstraZeneca and Sanofi’s Beyfortus leads the way. It achieved sales of 547 million euros ($592 million) in 2023.
While cross-trial comparisons carry inherent problems such as differences in patient populations and endpoints, Beyfortus, in its phase 3 study, showed an ability to reduce the incidence of medically attended lower respiratory tract infection caused by RSV by 74.9% compared to placebo.
Elsewhere, Pfizer’s vaccine Abrysvo, which pulled in $890 million in 2023, has been approved for pregnant women in the 32- to 36-week period of gestation.
GSK’s vaccine Arexvy, which generated sales of 1.2 billion pounds sterling ($1.5 billion) in 2023, has been approved only for adults.