Retrospective test-negative case-control study across 9 Australian hospitals evaluating maternal RSVpreF (bivalent prefusion F protein) vaccine effectiveness (VE) against RSV hospitalization in infants ≤6 months old, from March 2025 through February 2026 — the first full year after Australia added RSVpreF to its National Immunization Program at ≥28 weeks' gestation.
Among 655 infants hospitalized with lower respiratory tract disease (LRTD), VE against RSV-LRTD hospitalization was **77.8%** (95% CI, 66.4%–85.3%) for infants 0–6 months, rising to **86.3%** (95% CI, 79.0%–91.1%) for those 0–2 months. VE against severe RSV-LRTD was 80.4% (95% CI, 54.4%–91.6%) and against RSV-ARI hospitalization was 80.8% (95% CI, 70.4%–87.6%). Severe LRTD occurred in 32% of infants born to unvaccinated mothers vs. 17% born to vaccinated mothers.
- Retrospective case-control design limits causal inference and is subject to residual confounding. - Relatively small sample size for subgroup analyses; authors note future larger studies are needed for additional subgroup VE estimates. - Healthy vaccinee bias is possible, as vaccinated mothers may differ systematically from unvaccinated mothers.
Maternal RSVpreF vaccination at ≥28 weeks' gestation provides strong, year-round protection against RSV hospitalization in infants through 6 months, with the greatest benefit in the first 2 months of life. Clinicians should counsel pregnant patients on the importance of timely RSVpreF vaccination to maximize neonatal protection when infants are most vulnerable.
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