A single intramuscular injection of the monoclonal antibody nirsevimab reduces respiratory syncytial virus (RSV) infection in pre-term infants by 70% compared with placebo, trial results show.

In the trial, more than 1400 babies born between 29 weeks and 34 weeks and six days were randomised in a two-to-one ratio to a 50mg nirsevimab injection or placebo saline injection, respectively.

The babies, at 164 sites across 23 countries including Australia, received their injections in the two months prior to the autumn and winter RSV season.

During the five-month follow-up after vaccination, 9.5% of babies given placebo had an RSV-associated lower respiratory tract (LRT) infection requiring medical attention compared with just 2.6% of those given nirsevimab, the study authors reported in the New England Journal of Medicine.