An evaluation of 2015-2019-2019 United States respiratory syncytial virus hospitalizations as a framework to develop potential strategies for the preventiosn of the hospital burden among infants

Background New options for RSV prevention are available for the 2023/2024 RSV season, nirsevimab, a monocolonal antibody, and RSVpreF maternal vaccine, that target infants entering their first RSV season. Countries vary in implementation of one or both strategies to reduce the RSV burden among infants. Methods This study utilized retrospective cohort data from 47 children's hospitals in the United States Pediatric Health Information Systems (PHIS) database between 2015 and 2019. Patients hospitalized with RSV or bronchiolitis aged 0-15 months were included based on birth timing relative to the RSV season. Annualized hospitalization rates per 100,000 were calculated from extrapolated population estimates. Recommended prevention strategies were applied to age cohorts to compare protection afforded by nirsevimab and maternal immunization strategies. Findings 72,209 RSV hospitalizations were included in the study. Compared to those born nine months prior to the season (n = 2116; 375/100,000 per year), those born at the start of the season were 9.44 (9.02-9.89) times as likely to be hospitalized for RSV (n = 19,979; 3542/100,000 per year). Both strategies would prevent most of these hospitalizations. Maternal immunization would not prevent hospitalizations of infants aged two or 3 months at season start, who were respectively 2.95 (2.80-3.10) and 2.22 (2.11-2.34) times as likely to be hospitalized. Proportionally more preterm infants were hospitalized in their second RSV season, resulting in less protection (up to 40% to >80% unprotected). Interpretation These findings suggest without a more narrowly targeted strategy, current nirsevimab recommendations may not be as cost efficient for infants born further outside of the RSV season, and those born later in the season who are more likely to be hospitalized in subsequent seasons. Conversely, it may be more beneficial to begin maternal immunization further in advance of the season. Immunization strategies should be based on the RSV seasons within specific regions.