Nirsevimab
Immunoglobulins and antitoxins
Immunoglobulins and antitoxins
Long-acting antibody injected once into infants to protect them through the RSV season; it gives ready-made immunity and is not a vaccine.
Also called: nirsevimab-alip
Quick facts
- Group
- Immunoglobulins and antitoxins
- Target
- Fusion (F) protein of respiratory syncytial virus
- Key effects
- Pain · Rash
- Monitor
- Signs of bleeding at the site
- ATC
- J06BD08
No doses: the clinician sets them by the current guideline.
Mechanism of action
The figure shows the RSV F protein bound to MEDI8897, the research name of nirsevimab.
Nirsevimab is a human monoclonal antibody against the F protein that RSV uses to fuse with the cells of the airway. By binding F it stops the virus from entering and infecting cells. It was engineered to be long-acting, so one injection covers a typical RSV season. Protection is passive: the antibody itself protects, and the infant's immune system is not activated or trained.
- Binds the F (fusion) protein on the surface of RSV
- F can no longer fuse the virus with airway cells
- Infection and spread to the lower airways are blocked
- Long-acting design keeps it protective through the season
Indications
- Prevention of severe RSV lower respiratory tract disease in infants born during or entering their first RSV season Bronchiolitis (RSV) →
- Children up to their second season who remain at increased risk (for example chronic lung disease or severe immunocompromise) Bronchiolitis (RSV) →
Adverse effects
Common
- Pain, swelling or hardness at the injection site
- Rash, uncommon
Contraindications
- History of a severe allergic reaction (anaphylaxis) to nirsevimab or any component
Key interactions
- Routine childhood vaccines, including live vaccines
- Can be given at the same visit, at a different site; no interval is needed.
- Maternal RSV vaccine during pregnancy
- Most infants need one or the other, not both; if the mother was vaccinated well before birth the antibody is usually not needed.
What is monitored
- Observation after the injection for allergic reactions
- Signs of bleeding at the site in infants with low platelets or clotting disorders
Administration and safety
- Single intramuscular injection by a trained health worker
- Ideally given in the birth hospitalisation or the first week of life for infants born in the season, or just before the season starts
- Usually deferred in a moderate or severe acute illness
- It is an antibody, not a vaccine: the record states the product given
Pregnancy and breastfeeding
Not given in pregnancy: it is given to the infant. The alternative strategy is RSV vaccination of the mother during pregnancy.
Nursing care
- Ask whether the mother received an RSV vaccine in pregnancy and when
- Ask about bleeding disorders, low platelets or anticoagulants
- Explain to parents that it gives ready-made protection and does not prevent all colds
- Teach signs that need urgent care: breathing difficulty, bluish lips, poor feeding
Pharmacokinetics
- Absorption
- Given by intramuscular injection.
- Half-life
- Long-acting by design: one dose protects through a typical RSV season.
Test yourself
Think of the answer, then tap the question to see it.
Which RSV protein does nirsevimab target?
The fusion (F) protein in its prefusion form, which the virus needs to enter airway cells.
Is nirsevimab a vaccine?
No. It is a monoclonal antibody that gives passive, ready-made protection without training the infant's immune system.
How many injections of nirsevimab are usually needed for one RSV season?
Usually one: it is a long-acting antibody designed to protect through a typical season.
Does an infant usually need nirsevimab if the mother received the RSV vaccine well before birth?
Usually not: most infants need either the maternal vaccine or the infant antibody, not both.
Connections
← Back to the class: Immunoglobulins and antitoxins
Educational content on how drugs work; not a prescribing guide and no substitute for a health professional's advice. No doses are given.
Sources: RSV Immunization Guidance for Infants and Young Children (Centers for Disease Control and Prevention (CDC), 2026); Nirsevimab-alip: MedlinePlus Drug Information (MedlinePlus (U.S. National Library of Medicine), 2026); Crystal Structure of RSV F A2 Bound to MEDI8897 (RCSB Protein Data Bank, 2026); ATCDDD - ATC/DDD Index (WHO Collaborating Centre for Drug Statistics Methodology, 2026).
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Representative model, for educational purposes only.