What is the approved age range and dosing schedule for Beyfortus (nirsevimab) respiratory syncytial virus vaccine?

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Last updated: March 16, 2026 • View editorial policy

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Beyfortus (Nirsevimab) Age Range and Dosing

Beyfortus is approved for infants from birth through 24 months of age, with specific dosing based on RSV season, body weight, and risk factors. 1

Age Range and Indications

First RSV Season

  • All infants aged <8 months born during or entering their first RSV season should receive nirsevimab 2
  • Administration can begin from birth for infants born during RSV season 1
  • For infants born outside RSV season, administer once prior to season start 1

Second RSV Season

  • Children aged 8-19 months who remain at increased risk for severe RSV disease entering their second RSV season 2
  • FDA approval extends to children up to 24 months who remain vulnerable to severe RSV disease 1

Dosing Schedule

First RSV Season - Weight-Based Dosing

  • <5 kg body weight: 50 mg as single IM injection 2, 1
  • ≥5 kg body weight: 100 mg as single IM injection 2, 1
  • Administered as one dose per RSV season 2

Second RSV Season - Fixed Dosing

  • 200 mg total dose administered as two separate 100 mg IM injections at different injection sites 2
  • Given regardless of body weight for children up to 24 months at increased risk 2, 1

Timing of Administration

Seasonal Timing

  • October through end of March in most of continental United States based on pre-COVID patterns 2
  • Administer shortly before or during RSV season for optimal protection 2
  • Infants born shortly before or during RSV season should receive nirsevimab within 1 week of birth 2

Special Populations

  • Premature infants with prolonged hospitalizations: Administer shortly before or promptly after hospital discharge 2
  • Tropical climates (southern Florida, Guam, Hawaii, Puerto Rico, U.S. territories): RSV seasonality may differ; consult local guidance 2
  • Alaska: Less predictable seasonality with longer duration; adjust based on local epidemiology 2

Special Dosing Considerations

Cardiac Surgery with Cardiopulmonary Bypass

First RSV Season:

  • If surgery within 90 days after receiving nirsevimab: Give additional weight-based dose 1
  • If surgery >90 days after receiving nirsevimab: Give 50 mg regardless of weight 1

Second RSV Season:

  • If surgery within 90 days after receiving nirsevimab: Give 200 mg regardless of weight 1
  • If surgery >90 days after receiving nirsevimab: Give 100 mg regardless of weight 1

Important Clinical Pearls

Administration Details

  • Can be administered during birth hospitalization or outpatient setting 2
  • Can be coadministered with routine childhood vaccines using separate syringes at different injection sites 2, 1
  • Preferably inject in anterolateral aspect of thigh; avoid gluteal muscle due to sciatic nerve risk 1

Common Pitfalls to Avoid

  • Do not administer palivizumab to infants who already received nirsevimab in same season 1
  • Only one dose per RSV season is recommended 2
  • Not recommended for prevention of hospital-acquired RSV infection 2
  • Nirsevimab may be given to children who received palivizumab in their first season when entering second season 1

Contraindications

  • History of serious hypersensitivity reactions including anaphylaxis to nirsevimab or any excipients 1
  • Use with caution in bleeding disorders or anticoagulation therapy 1

References

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Professional Medical Disclaimer

This information is intended for healthcare professionals. Any medical decision-making should rely on clinical judgment and independently verified information. The content provided herein does not replace professional discretion and should be considered supplementary to established clinical guidelines. Healthcare providers should verify all information against primary literature and current practice standards before application in patient care. Dr.Oracle assumes no liability for clinical decisions based on this content.