CLINICAL QUESTION: How effective is nirsevimab at preventing respiratory syncytial virus (RSV) lower respiratory tract disease (LRTD), hospitalizations related to RSV, and any RSV infection?
BACKGROUND: RSV is the most common cause of lower respiratory tract infection in children, with severe infections often requiring nirsevimab, a long-acting monoclonal antibody, which prevents hospitalizations related to RSV lower respiratory tract infections. Less is known about the effectiveness of nirsevimab to prevent mild disease or illness altogether.
STUDY DESIGN: Retrospective cohort study
SETTING: Kaiser Permanente Northern California (integrated healthcare delivery system)
SYNOPSIS: This study aimed to compare the risk of RSV LRTD among infants who received nirsevimab versus those who did not, adjusting for sex, race, and/or ethnicity. Of the 31,900 term infants included, almost half (15,647) received nirsevimab. Nirsevimab was 87.2% effective against RSV with LRTD, 98% against hospitalized RSV LRTD, and 71% effective against PCR-confirmed RSV infection. Nirsevimab-immunized infants with RSV LRTD had fewer encounters and lower odds of hospitalization than non-immunized infants. As this was an observational study, confounders that could increase a child’s risk of RSV, such as daycare attendance or having siblings, could not be taken into consideration. Additionally, this study did not include premature infants or those with high-risk conditions, limiting generalizability.
BOTTOM LINE: Nirsevimab is highly effective at preventing both mild and severe RSV-related illness in term infants.
CITATION: Hsiao A, et al. Effectiveness of nirsevimab against RSV and RSV-related events in infants. Pediatrics. 2025;156(2):e2024069510. doi: 10.1542/peds.2024-069510.
Dr. Kramer
Dr. Allen
Drs. Kramer and Allen are hospitalists at Nationwide Children’s Hospital and assistant professors of pediatrics at The Ohio State University College of Medicine, both in Columbus, Ohio.
