MATERNAL vaccination against respiratory syncytial virus (RSV) reduces the risk of hospitalisation in young infants by more than 80% when administered at least two weeks before birth, a major UK Health Security Agency (UKHSA) study presented at ESCMID Global 2026 on 18 April has found.
Whilst 55% of the cohort were infants born to unvaccinated mothers, they accounted for 87.2% of hospitalisations.
Matt Wilson, epidemiologist and lead author of the study, UKHSA, UK, said: “As the largest study to date examining the impact of this vaccine on infant hospitalisation, these findings provide robust evidence that vaccination offers substantial protection against severe illness in young infants.
“We found a clear relationship between timing and protection, with effectiveness increasing as the interval between vaccination and birth lengthens, reaching close to 85% when vaccination occurs at least four weeks before delivery.”
The Importance of Early Vaccination
A national maternal RSV vaccination programme was introduced in England on 1 September 2024, offering the Bivalent Prefusion F vaccine to pregnant women from 28 weeks’ gestation.
In this retrospective cohort study, UKHSA researchers used linked national datasets, including NHS maternity records, immunisation data, and hospital and laboratory data.
They analysed 289,399 infants born between 2nd September 2024 and 24th March 2025: around 90% of births in England during this period.
In total, 4,594 RSV-associated hospitalisations were recorded.
Infants whose mothers were vaccinated at least 14 days before birth experienced a vaccine effectiveness estimated at 81.3%, relative to the unvaccinated group.
Wilson continued: “While at least two weeks are typically needed for optimal protection, infants born 10 to 13 days after vaccination had around 50% fewer hospital admissions compared with those whose mothers were unvaccinated, whereas no reduction was seen when vaccination occurred less than 10 days before birth.
“This reinforces the importance of vaccinating as early as possible within the recommended window, while also showing that even when given later in pregnancy, some protection is still possible from around 10 days before birth, although earlier vaccination remains preferable.”
Vaccine Effectiveness in Preterm Infants
Vaccine effectiveness in preterm infants was estimated at 69.4%, when allowing at least 14 days between vaccination and birth.
“These findings are particularly important for preterm infants, who are among the most vulnerable to severe RSV infection,” Wilson added.
“With sufficient time between vaccination and birth, we saw good levels of protection in these babies.”
Implications for Perinatal Care
Researchers called for further investigation of both the maternal RSV vaccination programme on infant hospitalisation at a population level and how protection changes later in infancy.
UKHSA will reportedly be looking at maternal vaccination and monoclonal antibody immunisation effectiveness in very preterm infants, for whom both are recommended.
Wilson noted that survival from RSV bronchiolitis remains a major cause of infant mortality in low- and middle-income countries.
He said: “These findings underscore the potential benefits of wider rollout of maternal RSV vaccination globally in line with the World Health Organization’s recommendations.”
Reference
Wilson M et al. Maternal RSV vaccination and reduced risk of hospitalisation for babies in England – 2024/25. Oral presentation. ESCMID Global 2026, 17-21 April, 2026.
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