All Things RSV mAb

With a new respiratory syncytial virus (RSV) season quickly approaching, it can be helpful to have a quick review of the impact of RSV prevention efforts (and where we’re not making as much progress as we’d like).

First, a quick review of the products:

CDC will open ordering for RSV monoclonal antibody products (mAb) on August 1, 2026, with predetermined ordering thresholds that will be replenished monthly. 

• Nirsevimab (Beyfortus™, Sanofi Pasteur)  
  • 50mg/0.5mL pre-filled syringes (1- or 5-count package) for infants <5kg 
  • 100mg/mL pre-filled syringes (1- or 5-count package) for infants >5kg 
    • 200mg (100mg x 2) for high-risk infants 8-19 months entering their second RSV season 
  • Beyfortus™ is stored under refrigeration, has a shelf life of 36 months, and is stable at room temperature for 48 hours (recently increased from 8 hours) 
• Clesrovimab (Enflonsia™, Merck) 
  • 105mg pre-filled syringes (1- or 10-count package), regardless of weight 
  • Not indicated for infants entering their second RSV season 
  • Enflonsia™ is stored under refrigeration, has a shelf life of 30 months, and is stable at room temperature for 48 hours 

CDC RSVVaxView is a dashboard of the administration of RSV mAb products to infants ages 0-7 months for several jurisdictions. Only three jurisdictions reported infant RSV mAb administration rates over 50% for the 2025-2026 season; however, infants born to mothers who received an appropriately-timed* RSV vaccine during pregnancy are not eligible to receive RSV mAb. CDC estimates the coverage rate for maternal RSV vaccination to be 41.6%, for the 2025-2026 season, but there is wide variation based on geography and race/ethnicity.

Recommendations for administration of RSV mAb products can be found below:

• CDC guidance
• AAP guidance
  • AAP plans to release its updated policy statement and technical report for the 2026-2027 RSV season in early September

Last year, the Vaccine Integrity Project published a review of the evidence behind RSV mAb recommendations, along with a dashboard of the studies that were reviewed and links to published medical society guidelines.

RECENT STUDIES:

RSV mAb may provide better protection than maternal vaccination.

A study of 42,560 infants out of France compared the RSV-related hospitalization rates of infants of vaccinated mothers versus infants who received RSV mAb and found 55.9% of the 481 hospitalizations were among infants born to mothers who were vaccinated, compared to 44.1% of hospitalizations among infants who received RSV mAb. Infants who received RSV mAb were also less likely to be admitted to intensive care, require ventilator support, or require supplemental oxygen.

A second study from France, looked at 164,140 infants showed a 22% reduction in the odds of RSV-related hospitalization compared with maternal vaccination, but equal odds if maternal vaccine was given eight weeks or more prior to delivery (Note: the U.S. recommendation for maternal vaccination with Abrysvo™ is to administer between 32 and 36 weeks gestation, so this parity would be unachievable based on current U.S. recommendations).

Lastly, a study published in The Journal of Pediatrics by physicians at Mass General Brigham for Children showed some disparities in uptake of maternal RSV vaccination could be mitigated during the birth hospitalization, adding evidence to the notion that protecting vulnerable newborns against RSV during the birth hospitalization should be prioritized.

There is a wealth of evidence, both internationally and domestically, supporting the safety and effectiveness of RSV mAb products. As we approach year 4 of the use of these products, there needs to be continued focus on access and equity so every baby, regardless of insurance status or zip code, can have a shot at avoiding serious RSV disease.

*”appropriately timed” is administered to those who are 32-36 weeks gestation between the months of September and January and at least 2 weeks prior to delivery”