The UK introduced maternal bivalent RSVpreF vaccination at 28 weeks or more in late 2024, and replaced palivizumab with nirsevimab for high-risk infants a year later. This study measured what that programme actually delivered once it had settled into routine.
It was a national prospective test-negative case-control study at 37 hospital sites. Infants aged 6 months or under admitted with acute lower respiratory tract infection and tested for RSV were enrolled between September 2025 and January 2026; 694 entered the primary analysis, 429 RSV-positive and 265 RSV-negative. Effectiveness was adjusted for site, calendar month, gestational age, socioeconomic status, age at admission and breastfeeding.
Adjusted vaccine effectiveness against RSV hospital admission was 61% (95% CI 38 to 75) for infants up to 6 months and 76% (54 to 87) for infants up to 3 months. The whole programme, including infant monoclonal antibody, achieved 61% (39 to 75) through 6 months.
The age gradient is the clinically useful part. Protection is strongest exactly when RSV is most dangerous — the first weeks of life, when a bronchiolitic infant is most likely to need respiratory support. It wanes across the first six months, as transplacental antibody does, which is what the biology predicts and what the numbers show.
For Indian practice the relevance is anticipatory rather than immediate. Maternal RSV vaccination is not part of the national schedule, and RSV bronchiolitis fills paediatric wards every monsoon and winter without any preventive option beyond hand hygiene and breastfeeding. These are the effectiveness numbers that a cost-effectiveness case would eventually be built on, and they are strong.
- Where maternal RSV vaccination is available, give it from 28 weeks — protection is highest in the first three months of life
- An infant whose mother was vaccinated in pregnancy does not routinely need monoclonal antibody as well
- Expect protection to wane across the first six months; a 5-month-old with bronchiolitis is not a vaccine failure story
- Ask about maternal vaccination status when a young infant presents with bronchiolitis — it changes the pre-test probability of RSV
- Note the design: test-negative case-control, which controls for health-seeking behaviour but is not a randomised trial
The statistics, in plain English
A test-negative design compares vaccination rates between infants admitted with RSV and infants admitted with a similar illness that turned out not to be RSV. It is the standard method for vaccine effectiveness because both groups sought hospital care, which removes the biggest confounder — that vaccinated families may behave differently. The confidence intervals are wide (38 to 75 for the 6-month figure) because only 694 infants contributed, so the true effect could be around a third or around three quarters. The direction and the age gradient are secure; the exact number is not. Note that 78% of mothers were of White ethnicity, which limits how far the effectiveness estimate transfers.
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