Study: Nearly 80% of infants born in 2023-24 RSV season received RSV protection | Image Credit: © Peter Hansen - © Peter Hansen - stock.adobe.com.

Background

According to a research letter published in JAMA Network Open, nearly 80% of infants who were born amid the 2023 to 2024 respiratory syncytial virus (RSV) in a specific health care system received RSV protection with nirsevimab (Beyfortus; Sanofi and AstraZeneca) or the maternal RSV vaccine RSVpreF (ABRYSVO; Pfizer).¹

Those measures to protect against the respiratory virus were approved in 2023 by the FDA. Nirsevimab, a monoclonal antibody, is approved to prevent RSV lower respiratory tract disease (LRTD) in neonates and infants entering, or born during their first RSV season aged younger than 8 months, or up to 24 months of age that remain vulnerable to severe RSV through their second season.^1,2

RSVpreF is approved for pregnant persons at 32 to 36 weeks' gestation.¹

Investigators sought to determine RSVpreF and nirsevimab uptake at Kaiser Permanente Northern California (KPNC), an integrated health care delivery organization during the early period of availability.¹

"Uptake of maternal vaccines against respiratory pathogens is lower among younger individuals and Black or Hispanic individuals," wrote the research letter authors. "We investigated uptake of RSVpreF and nirsevimab and sociodemographic factors associated with uptake within KPNC during the early period of availability."¹

Study details

The data-only study used electronic medial record data from infants born to mothers aged 15 to 49 years at KPNC from October 17, 2023 to March 31, 2024. Nirsevimab was available as of October 17, 2023, while RSVprF became available on October 25, 2023.¹

The investigative team calculated the percentage of infants who received nirsevimab, those born to mothers exposed to RSVpreF, infants exposed to both, and infants exposed to neither protection method.¹

"We compared maternal characteristics, including race and ethnicity (Asian, Black, Hispanic, White, and other [eg, American Indian or Alaska Native, Native Hawaiian or Pacific Islander]), age, parity, neighborhood deprivation index, insurance type, and prenatal visit frequency, among infants in different categories using χ² and Kruskal-Wallis tests," the letter stated.¹

P values were 2-sided with statistical significance set at P ≤ .05.¹

Results

In all, 17,251 infants (51.4% male) were included in the analysis. Of these, 77.5% received protection from either RSVpreF or nirsevimab. There were 5855 (33.9%) infants who were only exposed to the maternal vaccine, with a median gestational age of 34 weeks (32.6-36.0). Median time from RSVpreF to delivery was 34 days.1

Of the 13,366 infants who received protection, 40.9% received only nirsevimab, while 460 (2.7%) were exposed to both protection methods. Of these infants, 143 (31.1%) were born preterm and 111 or 24.1% were admitted to the NICU.¹

A majority of infants (74.5%) who were born October to November received nirsevimab. More than half (52.3%) of infants born January to March were exposed to the maternal vaccine.¹

"Uptake of RSVpreF and nirsevimab differed by maternal age and race. Infants of mothers aged younger than 25 years were less likely than infants of mothers aged 35 years or older to be exposed to only RSVpreF (26.4% [95% CI, 24.3%-28.4%] vs 37.9% [95% CI, 36.5%-39.4%]), but more likely to receive only nirsevimab (44.2% [95% CI, 41.9%-46.5%] vs 40.1% [95% CI, 38.6%-41.5%])," according to study results.¹

Nirsevimab and/or RSVpreF exposure was highest among infants born to Asian mothers (86.7% [95% CI, 85.7%-87.7%]) and lowest among infants of Black mothers (70.2% [95% CI, 67.3%-72.9%]).¹

"However," the authors noted, "the proportion receiving only nirsevimab was similar among infants of Black (42.3% [95% CI, 39.2%-45.4%]) and Asian (42.7% [95% CI, 41.2%-44.1%]) mothers and lower in infants of White mothers (36.6% [95% CI, 35.3%-37.9%])."¹

Conclusion

A limitation of the study was a population that was insured and may not be generalizable. Overall, the availability of 2 different RSV protection methods could have contributed to an increased proportion of infants protected from the respiratory disease, which "may help mitigate disparities."¹

References:

1. Jacobson KB, Watson AJ, Merchant M, Fireman B, Zerbo O, Klein NP. Uptake of Maternal RSV Vaccination and Infant Nirsevimab Among Infants Born October 2023 to March 2024. JAMA Netw Open. 2025;8(1):e2453696. doi:10.1001/jamanetworkopen.2024.53696

2. Fitch, J. Nirsevimab-alip FDA approved to prevent RSV in neonates, infants. Contemporary Pediatrics. July 17, 2023. Accessed January 8, 2025. https://www.contemporarypediatrics.com/view/nirsevimab-alip-fda-approved-to-prevent-rsv-in-neonates-infants