Study: Dual RSV immunization linked to low hospitalization rates

A nationwide cohort analysis from France found low rates of respiratory syncytial virus (RSV)–associated lower respiratory tract infection (LRTI) hospitalization among infants exposed to both maternal RSVpreF vaccination and passive immunization with nirsevimab during the 2024-2025 RSV season.¹

The research letter, published in JAMA Pediatrics, evaluated outcomes among infants who received dual RSV immunization in a setting where families could choose maternal vaccination, monoclonal antibody immunization, or both.

Investigators used data from the French National Health Data System, which includes health information for more than 99% of the French population.^1,2 The study included all infants born in mainland France between September 1 and December 31, 2024, who were exposed to both preventive approaches.

Maternal vaccination was considered optimal when administered between 24 and 36 weeks’ gestation and when delivery occurred at least 14 days after vaccination. Vaccination outside that window or delivery occurring within 14 days of vaccination was categorized as nonoptimal. RSV-associated LRTI hospitalization and death were tracked through February 28, 2025, corresponding to the end of the RSV epidemic season in France.

Among 297,295 immunized children during the study period, 3597 infants (1.2%) received dual immunization. The median gestational age was 38.4 weeks, median birth weight was 3110 g, and 48% of infants were girls. Optimal maternal vaccination occurred in 2602 infants (72%).

Investigators reported that 268 infants (10.3%) in the optimal vaccination group were considered at high risk for RSV bronchiolitis hospitalization, with most born preterm. Nearly all infants in both the optimal and nonoptimal maternal vaccination groups had received nirsevimab before the end of November 2024.

RSV hospitalization rates remained below 1%

Overall, hospitalization for RSV-associated LRTI occurred in 31 infants, corresponding to a rate of 0.86% (95% CI, 0.56%-1.16%). Among infants whose mothers received optimal vaccination, 23 infants (0.88%) were hospitalized for RSV-associated LRTI, compared with 8 infants (0.80%) in the nonoptimal vaccination group.

Among high-risk infants in the optimal maternal vaccination group, 2 infants (0.75%) were hospitalized for RSV-associated LRTI, while hospitalization occurred in 21 low-risk infants (0.90%). One death occurred in the study population during follow-up.

The investigators noted that the RSV epidemic peak in France occurred in mid-December 2024, after nearly all infants in the cohort had already received nirsevimab.

Authors call findings exploratory

In the discussion, the authors compared the findings with prior research evaluating passive immunization alone. They wrote, “In the passive immunization group, the hospitalization rate for RSV-associated LRTI was 1.0% in term infants and 1.1% in preterm infants.”

The authors added, “These figures are similar to the percentages observed in the current study.”

Investigators emphasized that the analysis was exploratory because it did not directly compare the different RSV prevention strategies. “However, it provides valuable data to guide research on preventive RSV immunization strategies in infants,” the authors wrote.

The authors also acknowledged several limitations, including the relatively small number of RSV-associated hospitalization events, particularly among high-risk infants. “This led to wider confidence intervals, rendering the study underpowered to detect modest but clinically meaningful benefits,” they wrote.

The investigators concluded that additional research is needed to determine whether dual immunization offers additional clinical value in populations at elevated risk for severe RSV disease. “Further research is needed to better clarify the added value of dual immunization, particularly in preterm infants, for whom immunization effectiveness may be reduced,” the authors wrote.

References

1. Tréluyer L, Bertrand M, Gabet A, et al. Dual immunization against RSV with RSVpreF and nirsevimab. JAMA Pediatrics. Published online May 18, 2026. doi:10.1001/jamapediatrics.2026.1346

2. Lassalle M, Zureik M, Dray-Spira R. Proton pump inhibitor use and risk of serious infections in young children. JAMA Pediatr. 2023;177(10):1028-1038. doi:10.1001/jamapediatrics.2023.2900