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Published on: November 1, 2011
Effectiveness of nirsevimab among infants in their first RSV season in the United States, October 2023-March 2024: a
Amanda B Payne1, Steph Battan-Wraith2, Elizabeth A K Rowley2
1National Center for Immunization and Respiratory Diseases, Centers for Disease Control and Prevention, Atlanta, GA, USA.
Insights
Nirsevimab effectively protected infants against RSV-associated emergency department visits and hospitalizations during their first RSV season. The monoclonal antibody showed high effectiveness, particularly in preventing hospitalizations.
Area of Science:
- Pediatrics
- Immunology
- Public Health
Background:
- The Centers for Disease Control and Prevention recommended nirsevimab for infants to prevent respiratory syncytial virus (RSV).
- Nirsevimab is a long-acting monoclonal antibody administered to protect infants during their first RSV season.
Purpose of the Study:
- To estimate the effectiveness of nirsevimab against RSV-associated emergency department (ED) encounters.
- To evaluate nirsevimab's effectiveness in preventing hospitalizations among U.S. infants during the 2023-2024 RSV season.
Main Methods:
- A test-negative analysis was conducted using electronic health record data from six healthcare systems.
- Infants aged under 8 months were included, comparing those who received nirsevimab with those who did not for RSV-like illness encounters.
- Effectiveness was adjusted for demographic factors and calendar day, excluding infants whose mothers received RSV vaccination during pregnancy.
Main Results:
- Nirsevimab demonstrated 77% effectiveness against RSV-associated ED encounters (95% CI: 69%-83%).
- Nirsevimab showed 98% effectiveness against RSV-associated hospitalizations (95% CI: 95%-99%).
- Effectiveness estimates were based on a median of 52 days (ED) and 48 days (hospitalization) post-administration.
Conclusions:
- Nirsevimab is effective in preventing RSV-associated ED encounters and hospitalizations in infants during their first RSV season.
- The highest protection was observed against RSV-associated hospitalizations.
- Continued monitoring is recommended to assess long-term effectiveness as time since nirsevimab administration increases.
Background:
In August 2023, the Centers for Disease Control and Prevention recommended nirsevimab, a long-acting monoclonal antibody, for all U.S. infants aged <8 months entering or born during their first respiratory syncytial virus (RSV) season. Our aim was to estimate nirsevimab effectiveness against RSV-associated emergency department (ED) encounters and hospitalisation among U.S. infants during the 2023-2024 RSV season.
Methods:
We conducted a test-negative analysis using electronic health record (EHR) data from 6 healthcare systems, including ED encounters and hospitalizations with a diagnosis of RSV-like illness (RLI) during October 8, 2023-March 31, 2024, among infants aged <8 months as of October 1, 2023, or born during the study period. Nirsevimab effectiveness was estimated by comparing children who received nirsevimab with those who did not among RSV-positive and RSV-negative encounters, adjusting for age, race and ethnicity, sex, calendar day, and geographic region and excluding infants whose mother received RSV vaccination during pregnancy.
Findings:
Among 5039 ED encounters with RLI among infants in their first RSV season, 2045 (41%) were RSV-positive and 446 (9%) received nirsevimab, with a median time since dose of 52 days (interquartile range [IQR]: 27-84 days). Among 1025 hospitalizations with RLI among infants in their first RSV season, 605 (59%) were RSV-positive and 95 (9%) received nirsevimab, with a median time since dose of 48 days (IQR: 24-82 days). Nirsevimab effectiveness was 77% (95% CI: 69%-83%) against RSV-associated ED encounters and 98% (95% CI: 95%-99%) against RSV-associated hospitalisation.
Interpretation:
Nirsevimab was effective in preventing RSV-associated ED encounters and hospitalisation among infants in their first RSV season, with greatest protection against hospitalisation. However, these estimates reflect a short interval from nirsevimab administration to RLI onset. Since nirsevimab is a passive immunization and concentration is expected to wane over time, it is important to continue monitoring effectiveness to assess effectiveness with increased time since dose.
Funding:
This work was supported by the Centers for Disease Control and Prevention (contracts 75D30121D12779 to Westat and 75D30123C18039 to Kaiser Foundation Hospitals).
