Nirsevimab immunization may significantly reduce RSV-related LRTI in high risk infants: JAMA

A nationwide case-control study from Chile published in the Journal of the American Medical Association revealed that nirsevimab immunization significantly reduced RSV-related lower respiratory tract infection (LRTI) hospitalizations in high-risk infants. The findings support shifting from targeted palivizumab prophylaxis to a broader, universal nirsevimab strategy for RSV prevention.

Respiratory syncytial virus (RSV) is a leading cause of lower respiratory tract infections (LRTIs) in infants around the globe, particularly dangerous for those born prematurely or with congenital heart disease (CHD). While nirsevimab has already demonstrated increased efficacy in healthy infants in clinical trials, evidence in higher-risk groups has been limited thus far.

Thus, this new case-control study examined the 2024 RSV season in the rollout of a universal immunization strategy. This research analyzed nationwide hospital data and compared 179 at-risk infants hospitalized with RSV-related LRTIs to 708 matched control infants who were not hospitalized. The study included infants born preterm (before 36 weeks gestation) or diagnosed with CHD, with further focus on those at highest risk extremely preterm infants (before 32 weeks) and those with heart conditions.

Among all at-risk infants, receiving a single dose of nirsevimab was associated with an 84.3% reduction in the risk of RSV-related hospitalization. The protective effect was even more pronounced in certain subgroups, where infants with CHD saw a 96.3% reduction in hospitalization risk, while those classified as high-risk overall experienced an 85.1% reduction.

In the group of infants born extremely preterm, the reduction in hospitalization risk was estimated at 65.9%, but the confidence interval was wide and included the possibility of no significant effect. This research caution that more data may be required to confirm effectiveness in this particularly vulnerable population.

This study highlighted the broad reach of Chile’s program, where nearly all infants in both the case and control groups had received nirsevimab. Still, a higher proportion of hospitalized infants had missed immunization when compared to controls, which reinforces the protective role of the intervention.

Traditionally, RSV prevention for high-risk infants has relied on targeted use of palivizumab. The Chilean experience suggests that replacing this targeted strategy with universal nirsevimab immunization could yield substantial benefits at the population level. Overall, the findings of this study suggest that universal programs could ease pressure on healthcare systems while improving outcomes for children most at risk.

Reference:

Sauré, D., Torres, J. P., Goic, M., Thraves, C., Pacheco, J., Burgos, J., Zgheib, A., Del Solar, F., Neira, I., O’Ryan, M., & Basso, L. J. (2026). Nirsevimab in high-risk infants in a respiratory syncytial virus prevention strategy. JAMA Network Open, 9(4), e266042. https://doi.org/10.1001/jamanetworkopen.2026.6042