Food and Drug Administration advisers on Thursday recommended approval of AstraZeneca and Sanofi’s treatment for respiratory syncytial virus infections in infants, likely paving the way for the agency to clear the drug later this year.
The advisory committee was tasked with reviewing the effectiveness and safety of the companies’ drug, a monoclonal antibody called nirsevimab that’s designed to prevent lower respiratory tract disease associated with respiratory syncytial virus, or RSV. The independent experts voted unanimously in support of the drug’s use in infants born during or entering their first RSV season, and 19-2 in favor of the drug being used for children up to two years old who are still vulnerable during their second season.
“For the population of people for whom there is no currently available medication, I think this is absolutely fantastic,” said Benjamin Wilfond, a panel member and a pulmonologist at Seattle Children's Hospital. “I'm really excited about the possibility of this being approved and available and used.”
The vote on nirsevimab is the latest development in a flurry of regulatory activity that has resulted in approvals for the first two RSV vaccines in older adults, developed by GSK and Pfizer. Pfizer also recently received advisory panel backing for its vaccine to be used in pregnant women and, in November, nirsevimab was approved in Europe under the name of Beyfortus.
AstraZeneca and Sanofi supported their application with data on nirsevimab’s effectiveness through 150 days post-treatment, and safety up to one year. Data showed that a single dose reduced the risk of medically attended lower respiratory tract disease by 70% in one study and by 75% in another.
Data from a larger study evaluating safety within high-risk infants, meanwhile, was published last month and showed a single dose was 83% effective in preventing hospitalization from RSV-related disease in infants under one year of age.
The drugmakers also compared nirsevimab to Synagis, an existing antibody treatment for RSV that’s limited to use in certain high-risk infants and requires monthly injections.
Safety results were “overall favorable,” according to FDA reviewers, showing that the rates of serious adverse events were similar between trials. The most common adverse events included rash and a fever. Two cases of low platelet counts were recorded in the larger safety trial, but weren’t linked to nirsevimab.
According to the Centers for Disease Control and Prevention, infants under six months old are at the greatest risk of severe disease caused by RSV, and almost all children will experience RSV before the age of two.
“Most babies hospitalized with RSV are born at term and healthy, which is why interventions specifically designed to protect all infants are likely to result in the greatest impact,” said Thomas Triomphe, head of vaccines at Sanofi, in a statement. “We are encouraged by the advisory committee’s positive vote based on the compelling clinical development program supporting nirsevimab and its breakthrough potential to reduce the magnitude of annual RSV burden.”
Panel members had no reservations about nirsevimab’s overall safety or efficacy, but did question the extrapolation of efficacy data to infants born prematurely. The experts noted how that data doesn’t take the place of actual effectiveness results and called for additional research.
The committee also questioned how maternal vaccination against RSV might affect use of nirsevimab, as testing excluded mothers who received an experimental RSV vaccine.
The FDA is expected to make a decision on approval by the end of September and has indicated it will work to speed its verdict to potentially clear the drug ahead of the 2023-2024 RSV season.
Analysts have forecast significant sales of nirsevimab. Michael Yee, an analyst at Jefferies, recently estimated in a research note that the drug may have $3 billion in annual peak sales potential given its “strong efficacy” in infants, and “could have much higher penetration than the maternal vaccines.”