What is the recommended use of Nirsevimab (anti-RSV monoclonal antibody) for preventing respiratory syncytial virus (RSV) infection in high-risk infants, such as those born prematurely or with underlying health conditions like heart disease or lung disease?

Nirsevimab for RSV Prevention in Infants

All infants younger than 8 months born during or entering their first RSV season should receive a single dose of nirsevimab, regardless of whether they are premature or have underlying conditions like heart or lung disease. 1, 2

Universal First-Season Recommendation

This represents a paradigm shift from the previous approach with palivizumab, which was restricted to only high-risk infants. The Advisory Committee on Immunization Practices (ACIP) now recommends nirsevimab universally for all infants <8 months during their first RSV season because:

• 79% of infants hospitalized with RSV have no underlying medical conditions, making risk-based targeting insufficient 1
• A single intramuscular injection provides protection for the entire 5-month RSV season (approximately 150 days) 3, 4
• Efficacy is 70-75% for preventing medically attended RSV lower respiratory tract infection and 62-78% for preventing hospitalization 4, 5

Timing and Administration

• Administer shortly before or during RSV season (typically October through March in most of the continental United States) 1, 2
• Do not wait for "peak season"—give at or before season onset for optimal protection 2
• Only one dose per season is needed 1
• Can be co-administered with routine childhood vaccines without increased adverse events 3

Dosing by Weight

• Infants <5 kg: 50 mg intramuscular injection 3
• Infants ≥5 kg: 100 mg intramuscular injection 3

High-Risk Infants: Same First-Season Approach

Premature infants and those with chronic lung disease or hemodynamically significant congenital heart disease receive the same single-dose regimen as healthy term infants during their first RSV season. 1, 2

The evidence is particularly strong for high-risk populations:

• Infants born ≤30 weeks gestation have three times the hospitalization rate of term infants 1
• Premature infants have higher ICU admission rates 1
• The phase 2b trial specifically demonstrated 70.1% efficacy in preterm infants (29-34 weeks gestation) 4
• Infants with chronic lung disease or congenital heart disease showed similar safety profiles and serum exposures 3

Special Considerations for Prolonged Birth Hospitalizations

• Infants with prolonged hospitalizations related to prematurity should receive nirsevimab shortly before or promptly after hospital discharge 1
• Nirsevimab is not recommended for prevention of hospital-acquired RSV infection (no evidence supports this use) 1

Second RSV Season: High-Risk Children Only

Children aged 8-19 months entering their second RSV season should receive nirsevimab ONLY if they remain at increased risk for severe RSV disease. 1, 2

This is a critical distinction—do not give second-season doses to healthy children without specific risk factors. 2

High-Risk Criteria for Second Season

Children who qualify include those with: 1, 2, 6

• Chronic lung disease of prematurity requiring medical support (oxygen, chronic corticosteroids, or diuretics) within 6 months before the second RSV season
• Hemodynamically significant congenital heart disease (moderate to severe disease, on medication for heart failure, or requiring surgery)
• Severe immunocompromise during RSV season
• Cystic fibrosis with manifestations of severe lung disease or weight-for-length <10th percentile
• American Indian or Alaska Native ethnicity (due to 4-10 times higher hospitalization rates in some populations) 1

Second-Season Dosing

• All eligible children aged 8-19 months receive 200 mg intramuscular injection 6

Geographic and Timing Variations

Adjust timing based on local RSV epidemiology, particularly in Alaska, Hawaii, Puerto Rico, U.S. Virgin Islands, Guam, and southern Florida where RSV patterns differ. 1

• Alaska has less predictable and often longer RSV seasonality 1, 2
• Tropical climates may have different or unpredictable RSV circulation patterns 1
• Consult state, local, or territorial guidance for these jurisdictions 1

Safety Profile and Contraindications

The safety data across 3,184 infants who received nirsevimab demonstrates: 7

• Most adverse events are mild to moderate and unrelated to treatment (≥98%) 7
• No treatment-related anaphylaxis or thrombocytopenia 7
• Deaths (<1% incidence) were all unrelated to treatment 7
• Adverse events of special interest occurred in <1% of recipients 7

Absolute Contraindication

Nirsevimab is contraindicated in persons with history of severe allergic reaction (anaphylaxis) to a previous dose or product component. 1, 6, 3

Precautions

• Follow ACIP general best practice guidelines for immunization in children with increased bleeding risk 1
• Use chronologic age (not corrected age) for preterm infants when determining eligibility 1

Common Pitfalls to Avoid

1. Do not restrict first-season nirsevimab to only high-risk infants—the recommendation is universal for all infants <8 months 1, 2
2. Do not give second-season doses to healthy children—this is only for specific high-risk populations 2
3. Do not delay administration waiting for peak season—protection requires time to develop, so give before or at season start 2
4. Do not confuse with palivizumab dosing—nirsevimab requires only one dose per season, not monthly injections 6
5. Do not use for treatment of active RSV infection—nirsevimab is for prevention only 8