Joanna Mulvaney PhD , 2025-05-01 14:24:00
A study published this morning in the Lancet Child and Adolescent Health, announces that the monoclonal antibody, nirsevimab, prevents severe respiratory syncytial virus infections in infants. In a huge review of the published evidence, epidemiologists from University of Toronto and York University, Toronto, tracked how effective nirsevimab was when prescribed in the community under real-world conditions.
According to the Toronto-based researchers, these observational findings bolster clinical trial data supporting the use of the drug to treat the respiratory virus. Researchers were not sure whether the drug designed to catch and block the RSV virus would work in ‘real life’ settings outside the strictly controlled environment of clinical trials. This newly combined data, the researchers claim, makes a case for routine use of nirsevimab in children too young to be vaccinated against RSV.
Respiratory syncytial virus is the leading cause of hospitalization of infants in the US. According to the CDC, 58,000–80,000 kids under five are admitted to hospital with the disease each year. Infants, children born prematurely, those with illnesses that affect the heart and lungs – for example cystic fibrosis, kids with weakened immune systems, and children with neuromuscular conditions that make swallowing difficult are especially at risk. While vaccines are very effective at preventing the most severe cases of the infection, kids who are too young to get vaccinated or who have compromised immune systems, are not well protected at present.
The researchers combined the results of 27 studies performed in Italy, France, Spain, Luxembourg and the USA demonstrating that using the monoclonal antibody-based drug reduced hospitalizations for RSV in infants under 12 months by as much as 83%.
At a more detailed level, the researchers concluded that in kids under a year old, intensive care admissions were reduced by 81%, and lower respiratory tract infections by 75%. The drug was slightly more effective for RSV in infants older than three months, preventing 83% of expected RSV-related hospitalizations compared to 76% in babies under three months old.
Monoclonal antibody drugs like nirsevimab are lab made antibodies designed to mimic our immune system. Rather than using a vaccine to help the immune system to recognize and fight off RSV, monoclonal antibodies get straight in there, binding to the viral particles and preventing them from infecting cells. For people who have no natural antibodies against RSV–like very young babies, the monoclonal acts to fight the virus while the immune system is playing catch up.
Sumsuzzman D, Wang Z, Langley JM, Moghadas SM. Real-world effectiveness of nirsevimab against respiratory syncytial virus disease in infants: a systematic review and meta-analysis. May 1st 2025.
