RSV Prophylaxis — Long-Acting Monoclonal Antibody Pregnancy: Paediatric use only — not applicable to pregnant women.

Nirsevimab

Brand names: Beyfortus

Adult dose

Dose: Not applicable — paediatric use only

Route: N/A

Frequency: N/A

Max: N/A

Paediatric use only.

Paediatric dose

Dose: <5 kg: 50 mg IM single injection. ≥5 kg: 100 mg IM single injection mg (weight-banded)/kg

Route: Intramuscular (anterolateral thigh preferred in neonates/infants)

Frequency: Single injection (covers one RSV season). Repeat annually if still in RSV risk period

Max: 100 mg

All infants up to 12 months entering their first RSV season. Also: children 12–24 months who remain at high risk (CHD, CLD, immunocompromised) during second RSV season. Administer before or during RSV season. Provides ~5-month protection from single dose. Does NOT require monthly dosing (unlike palivizumab). MHRA approved 2023. Source: BNF for Children 2024; NICE TA885.

Dose adjustments

Renal

No dose adjustment — weight-banded dosing only.

Hepatic

No dose adjustment required.

Paediatric weight-based calculator

Patient weight (kg)

Clinical pearls

MELODY trial (NEJM 2023): nirsevimab reduced RSV-associated lower respiratory tract infection (LRTI) leading to medical attendance by 74.5% vs placebo in healthy term and late-preterm infants. Single injection vs palivizumab's 5 monthly injections — transformative for RSV prevention logistics and programme delivery.
Replaces palivizumab for most infants: palivizumab (monthly IM × 5 doses) was limited to high-risk premature/CHD infants due to cost/dosing burden. Nirsevimab's single-dose protection enables universal infant RSV prophylaxis — JCVI and NHS England recommended universal programme from 2024–25 RSV season.
Extended half-life mechanism: nirsevimab contains a YTE (triple amino acid substitution) Fc modification extending half-life from ~21 days (palivizumab) to ~70 days. This enables single-season protection from one dose. Binds pre-fusion RSV F protein — more conserved epitope than palivizumab's binding site.
NICE TA885: recommended for all infants born during or entering their first RSV season, and for children up to 24 months who remain at high risk. NHS England programme provides nirsevimab through maternity services and community programmes.
Timing — before RSV season: administer in autumn (October–November in Northern Hemisphere). For babies born during RSV season — administer as soon as possible after birth. For babies entering second RSV season at high risk (premature, CHD, CLD) — can repeat annually. Source: BNF for Children 2024; Hammitt et al. NEJM 2022 (MELODY); NICE TA885; MHRA SPC Beyfortus.

Contraindications

Hypersensitivity to nirsevimab or excipients
Active RSV infection (treat infection first — prophylaxis not therapeutic)

Side effects

Injection site reactions (erythema, swelling — most common; mild, resolves in 24–48h)
Rash, fever (mild — reported in <5%)
Hypersensitivity reactions (rare — observe for 30 minutes post-injection)

Interactions

Live vaccines: no evidence of interference but separate by ≥2 weeks if possible
Palivizumab: do not co-administer — choose one or the other

Monitoring

Observe for 30 minutes post-injection (anaphylaxis rare but possible)
Injection site reaction (document, review at 48h if severe)
RSV season surveillance — if RSV LRTI develops despite nirsevimab, can still develop disease (not 100% protective) — monitor severity

Reference: BNF for Children 2024; Hammitt et al. NEJM 2022 (MELODY trial); NICE TA885; MHRA SPC Beyfortus; JCVI RSV immunisation programme 2024. Verify against your local formulary and the latest BNF before prescribing.

Curated clinical cross-links plus same-class fallbacks.

Calculators

Pathways