Respiratory syncytial virus (RSV) Infant Monoclonal Antibody Administration Extension

Kansas Health Alert Network (KS-HAN) Posted on March 23, 2026

Summary

In the continental United States, the recommended seasonal time frame for administration of RSV monoclonal antibodies typically starts in October and continues through March 31, with flexibility for public health authorities to adjust timing based on local RSV activity.

The RSV monoclonal antibodies nirsevimab (Beyfortus) and clesrovimab (Enflonsia) are recommended for all infants < 8 months born during or entering their first RSV season (who were not protected by maternal RSV vaccination during pregnancy), and nirsevimab is recommended for high-risk children 8–19 months entering their second RSV season.

RSV activity started late in Kansas this season, which suggests the risk of RSV infection may continue longer than usual into the spring.

Providers should extend the recommended timeframe for administration of nirsevimab and clesrovimab to eligible infants and young children for the prevention of severe RSV disease through April 30, 2026. Providers should use clinical judgment to weigh current and future risk of severe RSV disease, knowing that receipt of RSV monoclonal antibody at the end of the 2025-2026 season will preclude receipt of another dose at the beginning of the 2026-2027 season, except for high-risk children.

All other guidance for RSV infant monoclonal antibody administration remains unchanged at this time. KDHE will continue to monitor RSV activity in Kansas and will communicate additional information as needed.

Background

RSV monoclonal antibodies are typically recommended to be administered to eligible infants each RSV season from October 1 through March 31 in the continental U.S., with allowance for administration outside this time frame in tropical locations and Alaska, or in the setting of increased RSV activity outside typical months.

RSV activity in Kansas in the current 2025-2026 season began later than in recent past seasons, and RSV activity continues to be high (Figure 1). In the previous three seasons, RSV activity began increasing in September, October, and November, respectively, with peaks occurring within approximately a month before activity began to decline. In the current season, activity began increasing steadily in December 2025 (MMWR week 49), reached high levels and peaked at the end of February and into March (MMWR weeks 6–11). While some epidemiological metrics indicate that RSV activity may be declining, the duration and intensity of the remaining RSV season is currently unknown. Given the high risk of severe RSV disease among newborns and young infants, immunizing providers in Kansas should consider RSV monoclonal antibody administration through April 30, 2026. KDHE will continue to monitor RSV activity in Kansas and will communicate additional information as needed.

Figure 1. Weekly Percentage of Kansas Emergency Department Visits for Respiratory Syncytial Virus (RSV) Among Pediatric Visits (Patients < 13 Years)

Data Source: Kansas Department of Health and Environment, Kansas Syndromic Surveillance Program.

RSV Monoclonal Antibody Recommendations

Infants < 8 months: Administer one dose to infants born during or entering their first RSV season who are not protected already by maternal RSV vaccination during pregnancy.

• Nirsevimab: 50 mg for infants < 5 kg; 100 mg for infants ≥ 5 kg or

• Clesrovimab: 105 mg regardless of weight
  Children (8–19 months): Children entering their second RSV season who are at increased risk for severe disease (e.g., chronic lung disease of prematurity, severe immunocompromise, or cystic fibrosis) and American Indian and Alaska Native children should receive nirsevimab.

• Nirsevimab: 200 mg (administered as two 100 mg injections)
  Considerations for Clinicians

Providers should use clinical judgment to weigh current risk factors for severe RSV disease in the time that remains in the 2025-2026 season, including age and potential for exposure to RSV, against the future risk of severe RSV disease in the upcoming 2026-2027 season when deciding whether to immunize an eligible infant with nirsevimab or clesrovimab from April 1-30, 2026.

Receipt of RSV monoclonal antibody at the end of the 2025-2026 season will preclude receipt of another dose at the beginning of the 2026-2027 season, unless the child has risk factors that would make them eligible for a dose in their second RSV season.

RSV monoclonal antibodies can be administered simultaneously with other age-appropriate vaccines, including hepatitis B, influenza, and COVID-19.

In Kansas, recommended maternal RSV vaccination during pregnancy ended January 31, 2026. This administration window is not being extended.

For more information:

• Kansas Immunization Program: [email protected] or the Regional Nurse On-Call 877-296-0464 option 3.
• KDHE Epidemiology Hotline: [email protected] or 877-427-7317 (option 5)
• American Academy of Pediatrics RSV Immunization Administration Visual Guide
• Manufacturer information:
• Sanofi (nirsevimab/Beyfortus)
• Merck (clesrovimab/Eflonsia)

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