Merck’s experimental antibody for RSV reduced infants’ risk of certain lower respiratory infections by 60.4% compared to placebo, meeting the trial’s primary endpoint.
The Phase 2b/3 data, presented at IDWeek Thursday, will form part of Merck’s regulatory filing for clesrovimab. The numbers also offer an early look at how clesrovimab compares against AstraZeneca and Sanofi’s rival antibody Beyfortus.
While there are limits to comparing data across trials, Beyfortus was approved last year based on data showing it cut preterm infants’ risk of RSV-related lower respiratory tract infections requiring a physician’s visit by about 70% compared to placebo, according to the FDA. The risk reduction was about 75% in term and late preterm infants.
Differences in the clesrovimab and Beyfortus data may come down to how the primary endpoints were measured, Merck Research Laboratories’ SVP for infectious diseases and vaccines Paula Annunziato told Endpoints News.
In Merck’s trial, the endpoints were based on RSV infections where the patient had at least one indicator of disease or severity, such as wheezing or crackles. Annunziato pointed to a post-hoc analysis that suggested clesrovimab reduced the risk of more severe infections (measured by two more indicators of lower respiratory infection and severity) by 88%.
“Once both nirsevimab and clesrovimab are in the marketplace, there will be a number of groups” comparing the drugs, Annunziato said, using the generic name for Beyfortus.
Annunziato said Merck is speaking with the FDA and other regulators around the world. The company is hoping for a 2025 approval in the US, which would potentially lead to a launch in time for the start of that year’s respiratory illness season in the fall, she said.
“We’re really focused on infants,” Annunziato said. “We hope that we will get to the point where babies all over the world can benefit from prevention of RSV.”
Merck also touted a key secondary endpoint: Clesrovimab reduced the risk of RSV-associated hospitalizations by 84.2% compared to placebo.
The RSV market continues to be closely watched, with Pfizer presenting data earlier Thursday on how its vaccine Abrysvo fared at preventing severe illness and hospitalizations.