Impact of Nirsevimab on Respiratory Hospitalizations in Infants

Practical Conclusion

The administration of nirsevimab during the first respiratory season in infants is associated with a 17% absolute risk reduction in hospitalizations due to lower respiratory tract infections during the second year of life, based on a multicenter case-control study conducted in Andalusia, Spain. The protective association was particularly pronounced among confirmed cases of respiratory syncytial virus (RSV), with a 25.4% absolute risk reduction, and among infants with a history of inhaler use before hospitalization, where the reduction reached 27.7%. This suggests relevant benefits extending beyond the season in which the drug is administered.

Methodology

The researchers conducted a community-based case-control study across nine tertiary pediatric hospitals in Andalusia, which included a total of 1,375 infants (275 cases and 1,100 controls matched by birth date and province), all born between April 1, 2023, and March 31, 2024, and eligible to receive nirsevimab during the 2023-2024 RSV season.

Cases were defined as infants hospitalized due to lower respiratory tract infection during the 2024-2025 season (including bronchiolitis, bronchitis, pneumonia, bronchiolitis, or bronchospasm secondary to infection), while controls were selected from the community through their reference hospital, matched by birth date (with a maximum difference of 48 hours) and province of residence, with four community controls for each case.

The exposure assessed was the administration of nirsevimab during the 2023-2024 season, and the primary outcome was hospitalization for lower respiratory tract infection during the 2024-2025 season, analyzed using inverse probability weight models and augmented inverse probability weight models to estimate the average treatment effect, expressed as absolute risk reduction.

Exclusion criteria included having private health insurance, receiving a second dose of nirsevimab during the 2024-2025 season, and belonging to the high-risk infant group as defined by Andalusian immunoprophylaxis guidelines, such as those with certain underlying conditions that classify them at risk for RSV.

Data were collected from clinical records (hospitalization records for cases and periodic well-child visits in primary care, or emergency department or hospitalization records for controls) and laboratory tests, including variables such as locality size, prematurity, age at admission, birth cohort, and vaccination against flu, pneumococcus, and rotavirus, the latter used as a negative control.

Main Results

The administration of nirsevimab during the 2023-2024 season was associated with a 17.0% absolute risk reduction (95% confidence interval [CI]: 3.2%-30.8%) in hospitalizations due to lower respiratory tract infection during the 2024-2025 season, in the augmented inverse probability weight model, with a relative risk reduction of 46.4% (95% CI: 25.6%-67.2%) in the total sample.

Among confirmed cases of RSV, the protective association was more pronounced, with an absolute risk reduction of 25.4% (95% CI: 4.9%-45.8%), indicating a particularly marked benefit of nirsevimab in preventing RSV-related hospitalizations during the second respiratory season of life.

Infants with a history of inhaler use before hospitalization showed an absolute risk reduction of 27.7% (95% CI: 6.4%-48.9%); in the multivariable logistic regression model, this subgroup had an adjusted odds ratio of 0.44 (95% CI: 0.20-0.95), suggesting that children with respiratory history particularly benefit from nirsevimab beyond the season of administration.

The negative control exposure, vaccination against rotavirus, showed no association with the outcome (68.4% of cases and 69.3% of controls were vaccinated; p = 0.77), supporting the absence of significant residual confounding related to healthcare-seeking behavior.

Clinical Implications

“The administration of nirsevimab was associated with a reduction in hospitalizations due to lower respiratory tract infections in the second season, suggesting relevant benefits beyond the administration season, with potential implications for future cost-effectiveness evaluations,” the study authors wrote.

Limitations

The retrospective case-control design of the study presents inherent limitations that cannot be overlooked, including the possibility of residual confounding due to unmeasured variables such as household crowding, daycare attendance, presence of older siblings, parental tobacco smoke exposure, and family risk perception. Although the use of rotavirus vaccination as a negative control exposure reduced, but did not completely eliminate, the likelihood of relevant confounding related to health management behaviors. The high nirsevimab coverage in Andalusia (around 95%) resulted in a small sample size for the comparison group—children who did not receive nirsevimab—reducing the precision of estimates. Nonetheless, conclusive results were obtained both in inverse probability weight models and in augmented inverse probability weight models, as well as in classical logistic regression models for children with a history of inhaler use. RSV infection during the first season was not assessed due to expected etiological underdiagnosis, and the inclusion of lower respiratory tract infections not related to RSV in the primary outcome likely diluted the effect estimate—a bias towards the null value—given that nirsevimab specifically acts against RSV, which may explain the stronger association observed when restricting analysis to confirmed cases. Additionally, the study included only high-level hospitals, so infants hospitalized in lower-level centers may represent a different demographic than the general population of hospitalized children, although it’s likely that more severe cases were transferred to the participating tertiary centers.

Conflict of Interest

The authors declared no external funding for this study nor relevant conflicts of interest.

This content was developed using various editorial tools, including artificial intelligence, as part of the process. The content has been reviewed by a group of human editors prior to publication.

Fuente: https://espanol.medscape.com/viewarticle/nirsevimab-reduce-hospitalizaciones-respiratorias-lactantes-2026a1000umm