When should RSV (Respiratory Syncytial Virus) immunoprophylaxis with Beyfortus (nirsevimab) be given to children?

RSV Immunoprophylaxis (Beyfortus/Nirsevimab) Timing and Administration

Nirsevimab should be administered to all infants aged <8 months who are born during or entering their first RSV season, typically given from October through the end of March in most of the continental United States, with a single intramuscular injection shortly before or during the RSV season. 1

First RSV Season: Universal Recommendation

Age and Timing Criteria

• All infants aged <8 months born during or entering their first RSV season should receive nirsevimab 1
• Administration should occur shortly before or during the RSV season (typically fall through spring) 1
• In most of the continental United States, this translates to October through the end of March based on pre-COVID-19 pandemic RSV patterns 1

Weight-Based Dosing for First Season

• Infants weighing <5 kg receive 50 mg as a single intramuscular injection 2, 3
• Infants weighing ≥5 kg receive 100 mg as a single intramuscular injection 2, 3
• The injection should be administered in the anterolateral aspect of the thigh (avoid gluteal muscle due to sciatic nerve risk) 2

Clinical Impact

• This represents a major shift from palivizumab, which was only recommended for <5% of infants with specific high-risk conditions and required monthly dosing 1
• Nirsevimab demonstrated 79.5% efficacy against medically attended RSV lower respiratory tract infection in pooled trial data 3
• Protection extends through 150 days post-injection, covering an entire RSV season with a single dose 1, 4

Second RSV Season: High-Risk Children Only

Eligibility Criteria

• Children aged 8-19 months who remain at increased risk for severe RSV disease and are entering their second RSV season should receive nirsevimab 1
• High-risk groups include:
  • American Indian/Alaska Native children (who experience RSV hospitalization rates 4-10 times higher than other populations) 5
  • Children with chronic lung disease requiring medical intervention 1
  • Children with hemodynamically significant congenital heart disease 1
  • Children born at <29 weeks' gestation (extreme prematurity) 3

Dosing for Second Season

• All eligible children receive 200 mg regardless of body weight 2
• This is administered as two separate 100 mg intramuscular injections at different injection sites 2
• Children who received palivizumab in their first RSV season may receive nirsevimab in their second season 2

Special Populations and Circumstances

Cardiac Surgery with Cardiopulmonary Bypass

• Children undergoing cardiac surgery with cardiopulmonary bypass require an additional dose to maintain adequate serum levels 2
• First RSV season patients:
  • If surgery occurs within 90 days of receiving nirsevimab: give weight-based dose (50 mg if <5 kg, 100 mg if ≥5 kg) 2
  • If >90 days have elapsed: give 50 mg regardless of weight 2
• Second RSV season patients:
  • If surgery occurs within 90 days: give 200 mg regardless of weight 2
  • If >90 days have elapsed: give 100 mg regardless of weight 2

Geographic Considerations

• For American Indian/Alaska Native children in Alaska, consult state or local guidance on timing due to less predictable and often longer RSV seasonality 5
• The standard October-March window may need adjustment based on local RSV circulation patterns 5

Critical Implementation Points

Administration Logistics

• Nirsevimab can be co-administered with routine childhood vaccines using separate syringes at different injection sites 2
• Do not mix nirsevimab with any vaccines or medications in the same syringe 2
• The entire contents of the pre-filled syringe must be administered 2

Important Contraindications and Precautions

• Contraindicated in persons with history of severe allergic reaction (anaphylaxis) to a previous dose or product component 5
• Do not administer palivizumab to infants who have already received nirsevimab in the same season 2
• There are no data regarding substitution of nirsevimab for palivizumab once prophylaxis is initiated with palivizumab for the RSV season 2

Efficacy Against Severe Outcomes

• Recent 2024-2025 data demonstrates nirsevimab is 80% effective against RSV-associated ICU admission and 83% effective against acute respiratory failure requiring mechanical ventilation 6
• Protection was maintained when nirsevimab was received a median of 50-52 days before symptom onset 6

Common Pitfalls to Avoid

• Do not delay administration waiting for "peak" RSV season—give before or at the start of the season for optimal protection 1
• Do not restrict first-season nirsevimab to only high-risk infants; the recommendation is universal for all infants <8 months 1
• Do not use the wrong dosing syringe—verify the 50 mg (purple plunger) versus 100 mg (light blue plunger) pre-filled syringe matches the infant's weight 2
• Do not give second-season doses to healthy children without specific risk factors—this is only for high-risk populations 1