Beyfortus (Nirsevimab) Is Not Approved or Studied for Use in Adults
Beyfortus is exclusively indicated for infants and young children, and there is no safety or efficacy data supporting its use in adults. The medication should never be administered to adult patients.
FDA-Approved Indications Are Limited to Pediatric Populations
- Nirsevimab is approved only for infants <8 months born during or entering their first RSV season 1, 2
- A subset of high-risk children aged 8-19 months entering their second RSV season may also receive it 1, 2
- No adult population has been studied or approved for nirsevimab administration 1
Why Adults Should Not Receive Beyfortus
The pharmacology and dosing of nirsevimab are specifically designed for infant physiology:
- Weight-based dosing regimen: Infants <5 kg receive 50 mg; those ≥5 kg receive 100 mg 3
- The extended half-life monoclonal antibody targets neonatal Fc receptors (FcRn) that function differently across age groups 3, 4
- Clinical trials enrolled only infants and young children, providing zero safety data for adult administration 5, 3, 6
Potential Harms If Mistakenly Given to Adults
While no studies document adult administration, extrapolating from known mechanisms suggests potential risks:
- Severe allergic reactions including anaphylaxis are contraindicated in anyone with prior hypersensitivity to nirsevimab or its components 1, 2, 7
- Antibody-dependent enhancement (ADE) has been theoretically raised as a concern with RSV F protein antibodies, though incompletely assessed even in pediatric populations 4
- Unknown effects on adult immune system function, particularly given the high FcRn binding affinity that extends drug half-life 4
- Bleeding complications could theoretically occur, as special precautions are recommended even in children with bleeding disorders 1
Adults Need Different RSV Prevention Strategies
For adults ≥60 years requiring RSV protection:
- RSVpreF3 (Arexvy) or RSVpreF (Abrysvo) vaccines are the FDA-approved options for adults, not nirsevimab 8, 5
- These are single-dose intramuscular vaccines specifically studied in older adult populations 8, 5
Critical Clinical Pitfall to Avoid
Never confuse pediatric RSV prophylaxis (nirsevimab) with adult RSV vaccines - they are completely different products for different age groups with no interchangeability 8, 5.