At what age should Beyfortus (nirsevimab) be administered to infants?

Beyfortus (Nirsevimab) Age-Based Administration Guidelines

Beyfortus should be administered to all infants younger than 8 months of age who are born during or entering their first RSV season, and to children aged 8-19 months who are at increased risk for severe RSV disease entering their second RSV season. 1

First RSV Season: Infants <8 Months

• All infants younger than 8 months born during or entering their first RSV season should receive a single dose of nirsevimab, regardless of underlying health conditions 1
• This universal recommendation reflects that 79% of infants hospitalized with RSV have no underlying medical conditions 1
• Infants born shortly before or during RSV season should receive nirsevimab within 1 week of birth 1
• Administration can occur during the birth hospitalization or in the outpatient setting 1

Dosing by Weight for First Season

• Infants weighing <5 kg receive 50 mg as a single intramuscular injection 2
• Infants weighing ≥5 kg receive 100 mg as a single intramuscular injection 2

Second RSV Season: Children 8-19 Months

Only high-risk children aged 8-19 months entering their second RSV season should receive nirsevimab 1

High-Risk Criteria for Second Season

• Chronic lung disease of prematurity requiring medical support 3
• Severe immunocompromise 3
• Cystic fibrosis with severe lung disease or poor growth 3
• American Indian or Alaska Native children (due to 4-10 times higher RSV hospitalization rates) 4

Dosing for Second Season

• Children aged 8-19 months receive 200 mg (administered as two 100 mg injections at different sites simultaneously) 1

Timing Considerations

Optimal timing is shortly before the RSV season begins 1

• In most of the continental United States, administer October through end of March based on pre-COVID patterns 1
• Only one dose per RSV season is recommended 1
• Infants with prolonged birth hospitalizations should receive nirsevimab shortly before or promptly after hospital discharge 1

Geographic Variations

• Alaska: Less predictable seasonality with longer duration—consult local guidance 1
• Tropical climates (southern Florida, Guam, Hawaii, Puerto Rico, U.S.-affiliated Pacific Islands, U.S. Virgin Islands): Different or unpredictable patterns—consult state/territorial guidance 1
• Providers should adjust schedules based on local RSV epidemiology 1

Important Clinical Considerations

Coadministration with Vaccines

• Nirsevimab can be administered simultaneously with routine childhood vaccines at different injection sites 1
• Clinical trial data showed similar adverse event rates when coadministered versus vaccines alone 1
• Use chronologic age (not corrected age) for determining eligibility 1

Contraindications

• History of severe allergic reaction (e.g., anaphylaxis) to a previous dose or product component 3, 4

Not Indicated For

• Prevention of hospital-acquired RSV infection—no evidence supports this use 1
• Children ≥20 months have likely experienced two RSV seasons and are at decreased risk, thus not recommended 1

Key Efficacy Data Supporting These Recommendations

The age-based recommendations are supported by robust trial data showing nirsevimab reduces medically attended RSV lower respiratory tract infection by 79.5% and RSV-associated hospitalization by 77.3% in healthy infants 2. The number needed to treat is 14-24 to prevent one case of RSV requiring medical attention and 33-63 to prevent one hospitalization 5.