Glossary

Term · Baby Basics

nirsevimab

Also: Beyfortus, RSV antibody shot, RSV monoclonal antibody

A long-acting antibody given by injection to babies in their first RSV season to lower the chance of severe RSV lower respiratory illness.

In plain words

Nirsevimab is a monoclonal antibody. It is given as an injection to babies before or during their first respiratory syncytial virus season. That season is usually the fall and winter. RSV is a common virus. In young babies it can cause and pneumonia. The antibody lasts for several months. It gives the baby protection that the mother's body did not pass on. Trials found large drops in RSV illness that needed medical care. They also found fewer hospital stays. Nirsevimab is used to lower the chance of severe RSV illness. It is not a treatment for an active infection. Mothers are usually told about it at a pediatric visit. The decision is made together with the baby's clinician.

The deeper version

Nirsevimab is a long-acting, human IgG1 monoclonal antibody targeting the RSV fusion protein, with a supporting protection through a full season. In MELODY (Hammitt et al., New England Journal of Medicine 2022), among healthy late preterm and term infants, it reduced medically attended RSV lower respiratory tract infection by about 75 percent. HARMONIE (Drysdale et al., New England Journal of Medicine 2023) reported about an 83 percent reduction in RSV hospitalization in the first season, in a pragmatic, cluster-randomized design. The American Academy of Pediatrics and the CDC recommend it for infants under 8 months entering their first season, with timing set by birth season and region.

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Sources

  • Hammitt LL et al. — Nirsevimab for prevention of RSV in healthy late-preterm and term infants (MELODY). New England Journal of Medicine 2022
  • Drysdale SB et al. — Nirsevimab for prevention of hospitalizations due to RSV in infants (HARMONIE). New England Journal of Medicine 2023

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