💉 Nirsevimab and RSV: A Game-Changer in Infant Protection (2025 Update)

Published: July 2025 | By: FRCPathPrep.com Editorial Team

Essential for FRCPath Medical Microbiology Part 2 and infection prevention policy awareness

🦠 RSV: Why It Still Matters

Respiratory Syncytial Virus (RSV) remains a leading cause of bronchiolitis and lower respiratory tract infections in infants and young children. It also contributes significantly to hospital admissions, especially in the under-1-year age group during winter peaks.

For decades, Palivizumab was the only immunoprophylaxis option — limited to high-risk groups due to cost, dosing burden, and moderate effectiveness.

💉 Enter Nirsevimab: The New RSV Shield

Nirsevimab is a long-acting monoclonal antibody targeting the RSV fusion (F) protein, providing passive immunity with a single intramuscular dose. It was licensed in the UK in 2023 and has now been incorporated into routine immunisation strategies.

📌 What Makes Nirsevimab Different?

Feature	Nirsevimab	Palivizumab
Type	Long-acting monoclonal antibody	Monoclonal antibody
Target	RSV fusion (F) protein	RSV fusion (F) protein
Half-life	~100–150 days	~20 days
Dosing	Single dose IM	Monthly IM (5 doses per season)
Indication (UK)	Routine for infants born <6 months pre-season	High-risk infants only
Effectiveness	~80% reduction in hospitalised RSV LRTIs	~55% reduction in hospitalisation
Administration	Once, seasonal	Monthly injections during RSV season

🌍 UK Immunisation Programme (2025 Update)

According to JCVI and UKHSA (2025):

• Nirsevimab is now part of the national RSV immunisation programme for:

  • All infants born during or entering RSV season (Oct–March)

  • High-risk infants (e.g., congenital heart disease, CLD of prematurity)

  • Some preterm infants depending on timing of birth and risk

• Programme Type: Passive immunisation

• Delivery: Administered in maternity/neonatal units or primary care before RSV season

🧠 FRCPath Tip: This is not a vaccine — it is passive immunisation with a monoclonal antibody.

🌎 Global Perspectives (WHO & CDC)

Region	Recommendation Status	Notes
UK (JCVI/UKHSA)	Recommended and implemented (2023–2024 onwards)	Replaces Palivizumab in most infants
EU (EMA)	Approved	Country-level rollout ongoing
WHO	Endorses passive immunisation strategies	Supports for LMICs under review
USA (CDC/ACIP)	Recommended for all infants <8 months	Also given to certain high-risk 8–19 month-olds

🧬 How Does Nirsevimab Work?

• Binds to a highly conserved site on the RSV F protein

• Prevents viral fusion and entry into respiratory epithelial cells

• Provides protection for at least 5 months — enough to cover an RSV season

📉 Clinical Trial Highlights

• MELODY Trial:

  • Showed 83% reduction in RSV-associated LRTI hospitalisations

  • Included term and late preterm infants

• MEDLEY Trial:

  • Confirmed safety profile in infants eligible for Palivizumab

• Overall Tolerability: Excellent; mostly mild injection-site reactions

🏥 Microbiology & Infection Control Implications

Area	Relevance
Reduced RSV burden	Likely fewer RSV cases in infants during winter peaks
Diagnostics	Continue RSV PCR or rapid antigen testing in symptomatic infants
Infection control	RSV cohorting remains important during outbreaks, especially in NICUs
Lab advisory	Document immunisation status when interpreting results

📚 FRCPath Part 2 Exam Tips

• Understand difference between passive and active immunisation

• Be ready to advise paediatric teams or outbreak responders on:

  • Eligibility criteria for Nirsevimab

  • Infection prevention in nurseries, NICUs, and paediatric wards

• Know how Nirsevimab compares with Palivizumab — likely viva or short note topic

• Be familiar with JCVI/UKHSA 2025 RSV guidance

✅ RSV Immunisation Recommendations (UKHSA/JCVI 2025)

Agent	Brand Name	Recommendation
Nirsevimab	Beyfortus®	✅ First-line immunisation for eligible infants if available
Palivizumab	Synagis®	✅ Recommended only if Nirsevimab is unavailable

📌 Note: Both agents provide passive immunity. Only one is required per season, not both.

🔗 References

• UKHSA (2025). RSV: Nirsevimab Passive Immunisation Programme

• JCVI (2024–2025). Advice on RSV Immunisation in Infants

• WHO (2024). RSV Immunoprophylaxis Position Paper

• CDC/ACIP (2023). Nirsevimab Recommendations for Infants

🧠 Final Thought

Nirsevimab represents a paradigm shift in RSV prevention — offering broad, effective protection to infants with a single dose. For FRCPath candidates and microbiologists, understanding its role in immunisation programmes and outbreak dynamics is essential.

💡 Want high-yield immunisation updates and paediatric OSPE scenarios?

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