New preliminary study results suggest that new RSV antibody may help reduce infant hospitalisation due to RSV

Interesting first preliminary results from the HARMONIE phase 3b trial on the efficacy of Nirsevimab against RSV (respiratory syncytial virus) infection were presented at the 41st Annual Meeting of the European Society for Paediatric Infectious Diseases (ESPID) in Lisbon in early May.

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According to these initial results, a single intramuscular dose of this new monoclonal antibody would significantly reduce the frequency of hospitalisations in infants with RSV-associated lower respiratory tract infections (LRTI), suggesting that Nirsevimab could help reduce the overall burden of RSV disease.

The HARMONIE research study is investigating whether infants can be protected from severe disease caused by RSV infection by administering a single dose of monoclonal antibodies. The new, preliminary data from the HARMONIE real-world clinical trial suggests that in infants under 12 months of age who received a single intramuscular dose of nirsevimab, the number of hospitalisations due to RSV-related LRTI decreased by 83% (relative risk reduction, RRR) compared to infants who did not receive RSV treatment.

“RSV-related chest infections lead to high numbers of infants under 12 months old being hospitalized every year. These data reinforce the potential public health benefit of nirsevimab in terms of helping to reduce the strain on hospitals caused each year by RSV,” says Dr. Simon Drysdale, Consultant Pediatrician in Infectious Diseases at St. George’s University Hospital NHS Foundation Trust and Co-Chief Investigator of HARMONIE.

The reported outcomes are the first preliminary results presented at the ESPID 2023 congress. The corresponding abstract can be viewed in the official ESPID Abstract Book on page 123.

The HARMONIE study is still ongoing and will be fully completed and evaluated in the coming months. We will report in more detail once the full results and the accompanying publication are available.


The HARMONIE study is a collaboration between Sanofi and the National Institute for Health and Care Research (NIHR). Sanofi is a funder and sponsor of the study.