Nirsevimab

How it works

It is a humanised IgG1 monoclonal antibody that binds a conserved epitope on the prefusion form of the RSV fusion (F) protein, neutralising the virus and preventing fusion with and entry into host cells.

Prescribing in practice

• As with any biological agent, serious hypersensitivity including anaphylaxis is possible, so administer where reactions can be managed and avoid in known hypersensitivity to the product.
• It provides passive immunity for an RSV season as a single intramuscular dose, rather than active vaccination, so it confers no lasting immunological memory.
• Administer in line with the SPC and national immunisation guidance for the relevant infant cohorts.

Monitoring

Observe for immediate injection-site and hypersensitivity reactions after administration; no routine laboratory monitoring is required.

Counselling the patient

• Explain that this single injection helps protect the baby against severe RSV chest infection for the RSV season.
• It is given as a passive antibody and is not a routine childhood vaccine.
• Report any rash, swelling, breathing difficulty or signs of an allergic reaction after the injection.

Evidence & guidelines

Randomised trials (including the MELODY and HARMONIE studies) demonstrated that nirsevimab reduces medically attended and hospitalised RSV lower respiratory tract infection in infants, supporting its adoption in national RSV programmes.