Nirsevimab, a new monoclonal antibody treatment for respiratory syncytial virus, was 90% effective at preventing hospitalizations among infants this virus season, according to a March 7 CDC report.
The report offers the first real-world effectiveness data for the drug, which the FDA approved July 31.
"This finding supports CDC’s recommendation to protect infants in their first RSV season by giving the infant nirsevimab if the mother did not receive the maternal RSV vaccine during pregnancy," the agency said.
To assess the drug's real-world effectiveness, CDC researchers assessed the outcomes of 699 infants between October 2023 and February 2024 using the agency's New Vaccine Surveillance Network. The database tracks pediatric respiratory viruses at seven pediatric academic medical centers nationwide.
As nirsevimab did not hit the market until August, the analysis covers a shorter period of time than a normal RSV season. In the analysis, the median time between children receiving the drug and symptom onset was only 45 days, whereas a typical RSV season is about 189 days. The CDC noted the drug's effectiveness may be lower over full RSV seasons, as antibodies in the drug can decay over time.
In clinical trials, nirsevimab remained 81% effective at preventing hospitalizations in the 150 days after being administered to children.
See the full report here.