Bivalent prefusion F vaccine is effective in preventing RSV-LRTI hospitalizations in young infants.A large real-world study presented at ESCMID Global 2026 shows that maternal respiratory syncytial virus (RSV) vaccination reduces the risk of hospitalization in young infants.
“[Our study shows that] the bivalent prefusion F (PreF) vaccine is highly effective in preventing hospitalization due to RSV-associated lower respiratory tract infection in young infants in England’s maternal vaccination programme,” said lead author Prof Matt Wilson from the UK Health Security Agency, London, UK.
A total of 4,594 RSV-associated hospitalizations were reported. Of these, 87.2 percent (n=4,005) were from the unvaccinated group, representing a crude rate of 8/100 person-years (PY). Among infants whose mothers were fully vaccinated against RSV at least 14 days before birth, the corresponding rate was only 6.6 percent (n=302), translating to a crude rate of 1.1/100 PY.
After adjusting for covariates, vaccine effectiveness (VE) was 81.3 percent (p<0.0001) in the fully vaccinated vs the unvaccinated group. “While we did not specifically apply age constraints on this, this can be taken essentially as VE in the first 3 months of life,” Wilson said.
In the partially vaccinated group, the corresponding event and crude rates were 6.2 percent and 7.9/100 PY, respectively. [ESCMID Global 2026, abstract O0187]
There was also a clear association between timing and protection, with effectiveness increasing as the gap between vaccination and birth widens, Wilson said. The vaccine was most effective when given at least 4 weeks before birth (84.9 percent). At 14–27 days from vaccination to birth, VE was 73.1 percent.
Infants born 10–13 days after vaccination had 50 percent fewer hospital admissions than infants whose mums were unvaccinated. According to Wilson, this supports the use of opportunistic late-term vaccination.
“[These results] reinforce 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,” he continued.
“Late vaccination was common in this population and is associated with a disproportionately high risk of the outcome,” noted Wilson. Vaccination at 32–35 weeks’ gestation provided weaker protection than vaccination at 28–31 weeks (VE, –40.3 percent; p=0.02).
VE was 69.4 percent in all preterm babies (<37 weeks). “This is particularly important for preterm infants, who are among the most vulnerable to severe RSV infection,” Wilson said.
“With sufficient time between vaccination and birth, we saw good levels of protection in preterm babies. Giving the vaccination early in the third trimester, as recommended by the WHO, could protect most preterm infants,” he added. “Where possible, vaccination providers should seek to vaccinate pregnant women early in the licensed range of gestational weeks.”
RSV is a leading cause of infant hospitalization worldwide, with early-life infection linked to potential longer-term effects. [Curr Opin Infect Dis 2023;36:379-384; https://www.who.int/teams/global-influenza-programme/global-respiratory-syncytial-virus-surveillance, accessed April 29, 2026]
In the UK, RSV is a major cause of infant morbidity, with an annual average of 20,000 infant admissions during peak season and 7–8 deaths in hospitalized infants <6 months. [J Infect 2019;78:468-475; Lancet Public Health 2017;2:e367-e374]
A maternal RSV immunization programme was rolled out in September 2024 in England, offering the bivalent PreF vaccine to pregnant women from 28 weeks’ gestation. For this study, the researchers used routine data from the programme and a retrospective design to evaluate VE against RSV hospitalization in 289,399 infants. Of these, 55 percent comprised the unvaccinated group, 41.5 percent were in the fully vaccinated group, and 3.4 percent were in the partially vaccinated group.
“As the largest study to date evaluating the impact of this vaccine on infant hospitalization, these findings provide robust evidence that vaccination offers substantial protection against severe illness in young infants,” Wilson said in the press release. “Health professionals, pregnant women, and policymakers can be increasingly confident in the benefits of RSV antenatal vaccination.”
He called for more studies to evaluate the impact of the maternal RSV vaccination programme on infant hospitalizations at a population level. “Further work should assess the levels of protection later in infancy, and the effectiveness in programmes where monoclonal antibody immunization and maternal vaccination are in operational use, including in very preterm infants.”