- During the first RSV season in which a maternal vaccine and a monoclonal antibody for infants were available, 72% of infants were immunized, this study found.
- Disparities in access to immunization existed by race and ethnicity, with the lowest uptake among Black and Middle Eastern/North African mothers.
- The findings strongly suggested that clinicians and parents are following ACIP guidance.
During the first respiratory syncytial virus (RSV) season in which a maternal vaccine and a monoclonal antibody for infants were available, most infants were immunized via either intervention, according to an analysis of Vaccine Safety Datalink data.
Overall, 72% of 36,949 infants were immunized in the 2023-2024 RSV season with either the bivalent RSV prefusion F protein vaccine (Abrysvo) or nirsevimab (Beyfortus), Stephanie Irving, MHS, of the Kaiser Permanente Center for Health Research in Portland, Oregon, and colleagues reported in Pediatrics.
"This really is a success story," Irving told MedPage Today, "but it is important to also point out that more than a quarter of infants were not immunized against RSV."
The researchers also noted that there were disparities in access by race and ethnicity, with lowest uptake among Black (60.5%) and Middle Eastern/North African (60.2%) mothers. Rates were highest among Asian mothers (83.7%).
In an accompanying editorial, Natasha Halasa, MD, MPH, of Vanderbilt University Medical Center in Nashville, Tennessee, and colleagues said the findings "provide a crucial early assessment" of RSV immunization in the U.S. and represent "an encouraging level of early adoption" of these new tools.
However, they wrote, more research is needed to "identify barriers to equitable uptake."
In the summer of 2023, the FDA approved nirsevimab and the maternal RSV vaccine, both of which involve a single dose and offer seasonal RSV protection. CDC's Advisory Committee on Immunization Practices (ACIP) recommended both strategies independently -- but noted that nirsevimab isn't needed on top of maternal vaccination, unless a baby is born within 2 weeks of antenatal vaccination or is at high risk for severe RSV and would benefit from extra protection.
To assess uptake of interventions available during that first RSV season, Irving and colleagues assessed data from 10 of 11 Vaccine Safety Datalink sites, focusing on pregnancies that reached at least 32 weeks' gestation between Sept. 22, 2003 and Jan. 31, 2024, and ended in a live birth before April 1, 2024. Most pregnant women were between 25 and 34 years old, and were Hispanic or Latino (34.5%), white (29.9%), or Asian (17.8%).
Overall, more infants were protected via the monoclonal antibody (42.5%) than by maternal vaccination (32%). However, the distribution of RSV product shifted over the study period. Infants born September to December 2023 more often received nirsevimab, while those born January through March 2024 more often received antenatal vaccination, likely reflecting the timing of nirsevimab shortages and the rollout of the maternal vaccine, according to the researchers.
"Mothers who were vaccinated in the 32-to-36-week window in October went on to have babies in December, which is when we saw an increase in the number of infants immunized via antenatal vaccination," Irving said. "Babies born in the fall were born to mothers who didn't have an opportunity to receive the vaccine during pregnancy, and they chose to immunize via nirsevimab."
The study also strongly suggested that clinicians and parents are following ACIP guidance, with 95% of mothers receiving the vaccine within the recommended 32 to 36 weeks' gestation period. Also, of the 810 infants exposed to the maternal vaccine fewer than 14 days before birth, 72% subsequently received nirsevimab, as recommended by ACIP.
Despite the early good results, the editorialists noted that the COVID pandemic "has reshaped the landscape of vaccine acceptance, with patients expressing hesitancy toward newly introduced vaccines."
"The growing influence of social media misinformation, declining trust in public health institutions, and healthcare provider burnout further contribute to challenges in uptake," Halasa and colleagues warned.
Indeed, Cindy Prins, PhD, MPH, an infectious disease epidemiologist at the University of Central Florida College of Medicine, who was not involved in the study, agreed that the pandemic triggered an avalanche of misinformation and distrust in clinical research, and that vaccine hesitancy in pregnancy remains common.
Study limitations included that while the Vaccine Safety Datalink is "demographically representative," it may not reflect the broader pregnant population by race and ethnicity. In addition, sites mostly include patients who are privately insured, which could have limited the generalizability of the findings.
In addition, Prins noted that the 10 Vaccine Safety Datalink sites spanned most geographic regions except the South, which may have differing attitudes on vaccination.
Disclosures
The study was supported by the CDC.
Irving had no disclosures. Co-authors reported relationships with Pfizer, the NIH, the Garfield Memorial Fund, Hologic, and Johnson & Johnson.
The editorialists reported relationships with Sanofi, Quidel, Merck, and CSL Seqirus.
Primary Source
Pediatrics
Source Reference: Irving SA, et al "Infant respiratory syncytial virus immunization coverage in the Vaccine Safety Datalink: 2023-2024" Pediatrics 2025; DOI: 10.1542/peds.2024-070240.
Secondary Source
Pediatrics
Source Reference: Halasa NB, et al "Barriers to administering maternal RSV vaccination and monoclonal antibodies" Pediatrics 2025; DOI: 0.1542/peds.2025-070649.
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