ARGENTINA’S rollout of a maternal respiratory syncytial virus (RSV) immunisation programme has yielded promising early results, with new real-world evidence showing strong protection against RSV-associated lower respiratory tract disease (LRTD) and severe illness in infants during their first months of life.
Researchers conducted a multicentre, retrospective, test-negative case-control study (BERNI study) during the 2024 RSV season across 12 hospitals in Argentina. The study included infants aged ≤6 months who were hospitalised with LRTD between April and September 2024 and tested for RSV by PCR or immunofluorescence. Infants were classified as cases if RSV-positive, and controls if RSV-negative by PCR. Maternal vaccination with the bivalent RSV prefusion F vaccine (RSVpreF) was defined as administration between 32 and 36+6 weeks of gestation and at least 14 days prior to delivery. Vaccine effectiveness was calculated by comparing the odds of maternal RSVpreF vaccination among cases and controls, adjusted for potential confounders using multilevel logistic regression.
Of the 633 hospitalised infants screened, 505 met full inclusion criteria for the primary analysis. Among these, 286 tested positive for RSV and 219 tested negative. Maternal RSVpreF vaccination rates were significantly higher among controls (50%) than among RSV cases (18%). Vaccine effectiveness against RSV-associated LRTD requiring hospitalisation was 78.6% (95% CI: 62.1–87.9) from birth to 3 months and 71.3% (95% CI 53.3–82.3) from birth to 6 months. Effectiveness against severe RSV-associated LRTD requiring hospitalisation was 76.9% (95% CI: 45.0–90.3) through 6 months of age. All three RSV-related in-hospital deaths occurred in infants whose mothers had not received the vaccine during pregnancy.
These findings provide compelling evidence for the protective benefits of maternal RSVpreF vaccination during pregnancy and support continued implementation and international consideration of maternal RSV immunisation to reduce RSV-related infant morbidity and mortality.
Reference
Pérez Marc G et al. Real-world effectiveness of RSVpreF vaccination during pregnancy against RSV-associated lower respiratory tract disease leading to hospitalisation in infants during the 2024 RSV season in Argentina (BERNI study): a multicentre, retrospective, test-negative, case–control study. Lancet Infect Dis, 2025; DOI: 10.1016/S1473-3099(25)00156-2.
