Nirsevimab Protected Infants, Children From Severe RSV in 2023–2024 Season

During the 2023–2024 respiratory syncytial virus (RSV) season, New York City's Immunization Information System (IIS) reported that the administration of approximately 15,500 doses of nirsevimab, a highly effective immunization, protected infants and children aged 0 to 19 months from severe RSV.1

As the 2024–2025 RSV season approaches, ensuring an adequate supply of nirsevimab remains crucial for continued protection. | Image credit: Pawel - atock.adobe.com

The report is published in Morbidity and Mortality Weekly Report (MMWR).

“RSV infection is the leading cause of infant hospitalizations in the United States,” wrote the researchers of the study. “During the 2023–2024 RSV season, nirsevimab, a new, long-acting injectable human recombinant monoclonal antibody that prevents severe RSV infection in infants and young children became available.”

As the 2024–2025 RSV season approaches, ensuring an adequate supply of nirsevimab remains crucial for continued protection.

Nirsevimab is recommended for all infants younger than 8 months whose mothers did not receive the maternal RSV vaccine (Abrysvo; Pfizer) during pregnancy. It should be administered shortly before the start of the RSV season or within the first week after birth for infants born between October and March in most parts of the US. Additionally, nirsevimab is recommended for a select group of children aged 8 to 19 months who are at higher risk for severe RSV.2

The maternal RSV vaccine is recommended for individuals who are between 32 and 36 weeks pregnant during September through January in most parts of the US. It takes about 2 weeks after vaccination for these protective antibodies to develop and transfer to the baby. For those who have previously received the maternal RSV vaccine in an earlier pregnancy, the CDC currently advises against receiving another dose during subsequent pregnancies. Instead, these babies should be protected through the administration of nirsevimab.

This report aimed to evaluate the distribution and administration of nirsevimab, particularly in the context of a nationwide shortage that impacted both the commercial market and the Vaccines for Children (VFC) program.1 Given that approximately 75% of NYC’s children are eligible for public, no-cost immunizations through the VFC program, the NYC Health Department implemented a revised allocation strategy prioritizing VFC-eligible infants within the first week of life at birthing hospitals.

To assess the effectiveness of this strategy, the analysis examined data from the NYC Citywide Immunization Registry, focusing on reported nirsevimab doses stratified by VFC eligibility status, demographic characteristics, timing of administration relative to birth, and facility setting.

During the 2023–2024 RSV season, 15,521 nirsevimab doses were administered to infants and children aged 0 to 19 months in NYC, as reported to the Citywide Immunization Registry.

Among the 13,812 doses administered to infants born during the recommended period, 45% were given within the first week of life. This included 37% of VFC-eligible infants, 45% of non–VFC-eligible infants, and 61% of infants with unknown or missing VFC eligibility. Additionally, 18% of VFC-eligible infants received nirsevimab at their birthing hospital, compared with 8% of non–VFC-eligible infants and 38% of those with missing or unknown eligibility.

“Ensuring birthing hospital VFC enrollment and establishing protocols to offer nirsevimab to eligible infants before hospital discharge might increase nirsevimab administration within the first week of life,” wrote the researchers.

These findings underscore the importance of adequate supply and expanded VFC enrollment to improve early administration, particularly at birthing hospitals, for the 2024–2025 RSV season.

References

1. Askari MS, Oliver K, Benkel D, et al. Notes from the field: Rollout of nirsevimab to protect infants and young children during the respiratory syncytial virus season — New York City, 2023–2024. MMWR Morb Mortal Wkly Rep 2024;73:1107–1109. doi:10.15585/mmwr.mm7348a4

2. Immunizations to protect infants. CDC. News release. August 30, 2024. Accessed December 6, 2024. https://www.cdc.gov/rsv/vaccines/protect-infants.html