A new, population-level analysis of universal RSV immunization during the 2024–25 season found substantial reductions in RSV-related illness among infants when high coverage was achieved: a 42.7% drop in ED visits and a 46.5% drop in hospitalizations for RSV-related LRTI in infants under 12 months, with older children showing no similar declines.

Maternal RSV vaccination and nirsevimab together reduced medically attended RSV-associated ARI and RSV-related hospitalizations in US infants during the 2024–25 season, with reductions reaching about half compared with seasons before introduction.

In Spain, a primary study tracked 12,492 eligible infants and found that over 94% received nirsevimab, yielding an 86% drop in RSV-related LRTI hospitalizations in 2023–24 and a 55% drop in 2024–25 compared with pre-implementation seasons.

The study was led by Heidi L. Moline, MD, MPH, at the CDC, published online December 22, 2025 in JAMA Pediatrics and funded by the CDC, with limitations including potential lack of national representativeness and observational causality constraints.

A contemporaneous commentary notes that protection was sustained across two consecutive RSV seasons and through shifts from RSV-A to RSV-B, signaling a major turning point for infants and healthcare systems.

Experts emphasize the need for consistent, early immunization coverage in newborn cohorts to sustain reductions in severe RSV disease burden each season.

US data indicate prematurity as a significant risk factor, with preterm infants making up about 20% of RSV hospitalizations in children under 2 and facing longer stays and higher ICU/ventilation needs, underscoring ongoing importance of prevention products like nirsevimab for these infants.

First-season outcomes showed declines in first-time hospitalizations for LRTI, acute bronchitis, and bronchiolitis, and reductions in outpatient visits for wheezing, asthma, and bronchitis or bronchiolitis, though all-cause hospitalizations did not significantly decline in the second season.

The study utilized population-based surveillance across seven US pediatric centers, including over 5,000 children under 2 with medically attended ARI, to estimate the effectiveness of maternal vaccination (in infants under 6 months) and nirsevimab (in infants under 8 months as of Oct 2024).

Nirsevimab showed 77% effectiveness against medically attended RSV-ARI and 81% against RSV-associated hospitalization in the season studied, with peak protection in the first 30 days after administration and waning protection through 130–210 days, covering both RSV-A and RSV-B.