Merck says experimental RSV shot protected infants in trial, paving way for potential approval

• Merck said its experimental shot designed to protect infants from respiratory syncytial virus showed positive results in a mid- to late-stage trial.
• The pharmaceutical giant could emerge as a new competitor in the market for treatments against RSV, which causes hundreds of infant deaths each year.
• Merck is discussing the study data with regulators worldwide, with a goal of making the treatment available for infants as early as the 2025 to 2026 RSV season.

Merck on Thursday said its experimental shot designed to protect infants from respiratory syncytial virus showed positive results in a mid- to late-stage trial, bringing the company one step closer to filing for approval of the shot. 

The pharmaceutical giant could emerge as a new competitor in the market for treatments against RSV, which causes thousands of deaths among older Americans and hundreds of deaths among infants each year. Complications from the virus are the leading cause of hospitalization among newborns, making Merck's drug a valuable new treatment option if approved.

Merck plans to discuss the study data with regulators worldwide, with a goal of making the treatment available for infants as early as the 2025 to 2026 RSV season, according to a release. 

The trial examined the safety and efficacy of a single dose of the treatment, clesrovimab, in healthy preterm and full-term infants entering their first RSV season. Merck presented the results at the medical conference IDWeek in Los Angeles.

The treatment reduced RSV-related hospitalizations by more than 84% and decreased hospitalizations due to lower respiratory infections by 90% compared with a placebo among infants through five months, according to Merck. Clesrovimab also reduced lower respiratory infections that required medical attention by more than 60% compared with a placebo through five months.

RSV is a common cause of lower respiratory tract infections such as pneumonia. Results were consistent through both the five-month and six-month time points in the trial, Merck said.

The rates of adverse and serious side effects were comparable between patients who received Merck's shot and those who took placebos in the trial. There were no treatment or RSV-related deaths in the study, the company added. 

"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," Dr. Octavio Ramilo, chair of the Department of Infectious Diseases at St. Jude's Children's Research Hospital, said in Merck's release. Ramilo is also an investigator working on the trials. 

Merck's clesrovimab could potentially compete against a similar treatment from Sanofi and AstraZeneca called Beyfortus, which was in short supply nationwide last RSV season due to unprecedented demand. Both are monoclonal antibodies, which deliver antibodies directly into the bloodstream to provide immediate protection. 

But Merck's treatment can be administered to infants regardless of their weight, which the company said may offer convenience in terms of dosing. Meanwhile, the recommended dosage of Beyfortus is based on an infant's body weight. 

A Sanofi spokesperson said the dosage of Beyfortus was chosen "carefully through our clinical development and reflects the right dosage for each baby," with two different doses depending on whether they weigh more or less than five kilograms, or about 11 pounds. The implementation of those two doses was "managed effectively by providers" during the last RSV season, the spokesperson added.

Sanofi expects the U.S. market to have enough supply of Beyfortus during the current RSV season, which typically begins in the fall and lasts through the spring.

Last year, Pfizer rolled out an RSV vaccine that is administered to expectant mothers who can pass on protection to their fetuses.