Study: Three-quarters of infants protected against RSV last season
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Key takeaways:
- Three-quarters of infants were exposed to the maternal RSV vaccine or nirsevimab during their first RSV season.
- Younger mothers and Black mothers were less likely to receive the maternal vaccine.
Nearly 80% of infants born in a California health system were exposed to nirsevimab or the maternal respiratory syncytial virus vaccine in 2023-2024, the first season in which they were available, according to study findings.
The maternal vaccine, which is administered between 32 and 36 weeks’ gestational age, and nirsevimab, a monoclonal antibody recommended for infants up to age 19 months entering their first or second RSV season, are part of the “embarrassment of riches” the United States has to protect infants from severe RSV disease.
Karen B. Jacobson, MD, MPH, a research scientist in the Vaccine Study Center at Kaiser Permanente Northern California, and colleagues investigated uptake of these two immunizations within their health system from Oct. 17, 2023, to March 31, 2024.
Out of 17,251 infants (51.4% boys; mean maternal age, 31.2 years; standard deviation, 5.2 years), 77.5% were exposed to nirsevimab or the maternal vaccine, Jacobson and colleagues reported. One-third of infants (33.9%) were exposed only to the maternal vaccine a median of 34 days (interquartile range [IQR], 24-46 days) before birth. A larger proportion of infants were exposed to nirsevimab only (40.9%; median age, 4 days; IQR, 2-16 days).
According to the CDC, 17.8% of eligible pregnant women received the maternal RSV vaccine between Sept. 22, 2023, and Jan. 31, 2024, and 41.3% of women with an infant said their baby received nirsevimab before March 31, 2024. More recent data show that maternal vaccine coverage surpassed 35% among pregnant women since Dec. 7, 2024.
Some infants (2.7%) were exposed to both immunizations, of whom 31.1% were born preterm. According to the researchers, 72.7% of the 534 infants born within 2 weeks of their mother receiving the maternal vaccine also received nirsevimab, which aligns with CDC recommendations.
Compared with infants of mothers aged older than 35 years, infants of mothers aged younger than 25 years were more likely to receive nirsevimab (40.1%; 95% CI, 38.6%-41.5%; vs. 44.2%; 95% CI, 41.9%-46.5%) but less likely to be exposed to the maternal vaccine (37.9%; 95% CI, 36.5%-39.4%; vs. 26.4%; 95% CI, 24.3%-28.4%).
Infants of Asian women were most likely to be exposed to the maternal vaccine or nirsevimab (86.7%; 95% CI, 85.7%-87.7%), whereas infants of Black women had the lowest coverage (70.2%; 95% CI, 67.3%-72.9%), according to the authors. These figures mirror CDC data, which reported non-Hispanic Asian women had the highest uptake of the maternal vaccine and non-Hispanic Black women had the lowest (24.8% and 10.3%, respectively).
Infants of Black and Asian mothers had similar rates of nirsevimab uptake — 42.3% (95% CI, 39.2%-45.4%) and 42.7% (95% CI, 41.2%-44.1%), respectively, and rates were lower among infants of white mothers (36.6%; 95% CI, 35.3%-37.9%).
“Infants of younger mothers and Black mothers — historically undervaccinated groups — had lower overall RSV protection coverage, seemingly driven by discrepancies in maternal RSVpreF vaccination more than infant nirsevimab,” Jacobson and colleagues wrote. “The availability of two different RSV protection methods in sufficient supply may have contributed to an increased proportion of infants protected against RSV, which may help mitigate disparities.”
References:
- CDC. RSV immunization guidance for infants and young children. https://www.cdc.gov/rsv/hcp/vaccine-clinical-guidance/infants-young-children.html. Updated Aug. 30, 2024. Accessed Jan. 15, 2025.
- CDC. Weekly RSV Vaccination Dashboard. https://www.cdc.gov/rsvvaxview/data/index.html. Updated Aug. 27, 2024. Accessed Jan. 15, 2025.
- Jacobson KB, et al. JAMA Netw Open. 2025;doi:10.1001/jamanetworkopen.2024.53696.
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