Project Details

Clinical impact of RSVpreF maternal vaccine in infants of Argentina: An Active Surveillance Study

Julia Dvorkin, MD

Summary

BACKGROUND: In March 2024, Argentina became the first country to incorporate RSVpreF maternal vaccination into its national immunization program as a universal, free-of-charge primary intervention for pregnant individuals at 32–36.6 weeks' gestation. In 2025, the vaccination window was extended from six to ten months. GAP: Real-world evidence on the impact and effectiveness of RSVpreF maternal vaccination (MV) against severe RSV disease in young infants was lacking, particularly in low- and middle-income countries. HYPOTHESIS: MV with RSVpreF would lead to a significant reduction in RSV-related hospital admissions in infants in the Metropolitan Area of Buenos Aires (MABA), Argentina. METHODS: We conducted a multicenter, hospital-based surveillance study in four tertiary pediatric hospitals in the MABA (2018–2025). Population-level impact was assessed with a Poisson regression model. The model compared observed RSV-related acute lower respiratory tract infection (ALRTI) hospitalizations in infants aged ≤6 months with expected numbers based on pre-implementation seasons, using infants aged 12–18 months as a reference group. Vaccine effectiveness (VE) was estimated with a nested test-negative case-control design. RESULTS: RSV-related hospitalizations among infants aged ≤6 months decreased by 34.9% (95% CI 31.1-38.4) in 2024 and by 59.7% (57.3–61.9) in 2025, after the vaccination window was extended. The number needed to immunize to prevent one hospitalization fell from 83.9 in 2024 to 36.4 in 2025. In pooled 2024–2025 analyses, adjusted VE against RSV-related hospitalization was 73.7% (95% CI 58.3–83.6) in infants aged ≤6 months, and 78.5% (60.9–88.5) in infants aged ≤3 months. MV also protected against severe disease, with VE of 75.3% (39.1–90.4) against PICU admission and 80.9% (58.5–91.7) against prolonged hospitalization. No protection was observed when delivery occurred less than 15 days after vaccination. IMPACT: Universal RSVpreF maternal vaccination substantially reduced severe RSV disease in young infants in Argentina. Extending the vaccination window markedly increased its population-level impact. These findings provide real-world evidence to guide RSV prevention policies in Argentina and other low- and middle-income countries and highlight the need for complementary strategies for infants who remain unprotected.

Publications:

Razzini JL, Parada D, Solovey G, Guiñazú G, Sosa EM, Orta SR, Esposto S, Sanluis Fenelli G, Regalado AE, Torre V, Pichinenda M, Ossorio MF, Souto SM, Ojeda MN, Lugo S, Ferrero F, Polack FP, Dvorkin J, Caballero MT; RIMA Network Collaborators. Impact and effectiveness of RSV maternal immunization on infant hospitalizations in Buenos Aires: a hospital-based, multicentre, retrospective surveillance cohort study. Lancet Reg Health Am. 2025 Nov 19;52:101296. doi: 10.1016/j.lana.2025.101296. PMID: 41341162