A new multicenter UK study found that maternal vaccination against respiratory syncytial virus (RSV) reduced infant hospitalizations by 72%, with the greatest benefit seen when the vaccine was administered more than 14 days prior to delivery.
The test-negative, case-control study analyzed 537 mother–infant pairs across 30 hospitals between September 30, 2024, and January 20, 2025. All infants were born after the national RSV maternal vaccination campaign began—August 12 in Scotland and September 1 in England—and were younger than 6 months when admitted for acute lower respiratory infections, including bronchiolitis and wheezing.
The bivalent prefusion F (RSVpreF) vaccine demonstrated 72% effectiveness (95% confidence interval [CI] = 48%–85%) against RSV-associated hospitalization when given at least 14 days before delivery. Overall adjusted vaccine effectiveness, regardless of timing, was 58% (95% CI = 28%–75%).
Among the 537 infants, 297 (55%) were male and 240 (45%) were female. The median age at admission was 1.63 months (interquartile range [IQR] = 0.94–2.26) for RSV-positive infants and 1.41 months (IQR = 0.77–2.03) for RSV-negative controls. Maternal vaccination was documented in 73 (19%) RSV-positive infants and 60 (41%) RSV-negative infants.
No in-hospital deaths were reported. RSV-positive patients experienced more severe disease. Supplemental oxygen was required in 287 (73%) RSV-positive patients compared with 62 (43%) controls, and pediatric intensive care unit (PICU) admission occurred in 37 (9.5%) cases and 6 (4.1%) controls.
Among RSV-positive patients, those born to vaccinated mothers had similar clinical outcomes to those born to unvaccinated mothers. Median hospital stay was 4 days (IQR = 1–6) for vaccinated and 3 days (IQR = 2–5) for unvaccinated patients (P = .87). No statistically significant differences were found in respiratory support, PICU admission, or use of mechanical ventilation.
Unadjusted effectiveness of maternal vaccination in reducing high-flow nasal cannula use was 71% (95% CI = 47%–85%). For PICU admission, the estimated effectiveness was 64% (95% CI = 1%–87%), though the authors noted sample size limitations for these subgroup analyses.
The study adjusted for hospital site, calendar month, infant age, preterm birth, and sex. Pertussis vaccination served as a negative control and showed no protective effect (25%; 95% CI = –20% to 53%), supporting the validity of the findings.
“Our results are in a real-world setting and show similar effectiveness when measured at 14 days after vaccination to those seen in the MATISSE trial,” said Thomas C. Williams, PhD, of the University of Edinburgh, and one of the researchers.
The researchers emphasized that vaccination more than two weeks prior to delivery yielded greater protection, consistent with maternal antibody generation and placental transfer.
The study was funded by the National Institute for Health and Care Research, The Wellcome Trust, and Imperial College London. No conflicts of interest were reported.
Source: The Lancet Child and Adolescent Health