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Respiratory Syncytial Virus Disease Burden and Nirsevimab Effectiveness in Young Children From 2023-2024

Heidi L Moline^1,2, Ariana P Toepfer¹, Ayzsa Tannis¹

¹Coronavirus and Other Respiratory Viruses Division, National Center for Immunization and Respiratory Diseases, Centers for Disease Control and Prevention, Atlanta, Georgia.

JAMA Pediatrics

|December 9, 2024

Insights

New RSV prevention products like nirsevimab show high effectiveness in protecting infants from respiratory syncytial virus (RSV)-associated acute respiratory illness (ARI). This study highlights the potential public health impact of increased prevention product coverage.

Area of Science:

Pediatric Infectious Diseases
Immunology
Public Health Surveillance

Background:

Respiratory syncytial virus (RSV) poses a significant disease burden on young children.
New prevention products, including nirsevimab and a maternal RSV vaccine, were recommended for the 2023-2024 season.
Postlicensure studies are crucial for evaluating the real-world impact and effectiveness of these interventions.

Purpose of the Study:

To compare RSV epidemiology and disease burden in children under 5 during the 2023-2024 season versus prepandemic seasons (2017-2020).
To estimate the effectiveness of nirsevimab against medically attended RSV-associated acute respiratory illness (ARI).
To analyze nirsevimab binding site mutations in circulating RSV strains based on infant receipt status.

Main Methods:

Prospective population-based surveillance for medically attended ARI with molecular RSV testing.
Whole-genome sequencing of RSV-positive samples.
Test-negative case-control design to assess nirsevimab effectiveness in infants under 8 months.

Main Results:

RSV prevalence and hospitalization rates in 2023-2024 were similar to prepandemic levels.
Nirsevimab demonstrated 89% effectiveness against medically attended RSV-associated ARI and 93% against hospitalization.
No significant differences in nirsevimab binding site mutations were observed based on nirsevimab receipt.

Conclusions:

Medically attended RSV-associated ARI remains a substantial public health concern for young children in the US.
Nirsevimab offers significant protection against RSV-associated illness and hospitalization in infants.
Equitable and increased coverage of prevention products holds potential for substantial future public health benefits.

Read full analysis

Abstract

Importance:

During the 2023-2024 respiratory syncytial virus (RSV) season in the United States, 2 new RSV prevention products were recommended to protect infants in their first RSV season: nirsevimab and Pfizer's maternal RSV vaccine. Postlicensure studies are needed to assess prevention product impact and effectiveness.

Objective:

To compare the epidemiology and disease burden of medically attended RSV-associated acute respiratory illness (ARI) among children younger than 5 years during the 2023-2024 RSV season with 3 prepandemic RSV seasons (2017-2020), estimate nirsevimab effectiveness against medically attended RSV-associated ARI, and compare nirsevimab binding site mutations among circulating RSV in infants with and without nirsevimab receipt.

Design, Setting, And Participants:

This study included prospective population-based surveillance for medically attended ARI with systematic molecular testing for RSV and whole-genome sequencing of RSV positive samples, as well as a test-negative case-control design to estimate nirsevimab effectiveness. The study was conducted in 7 academic pediatric medical centers in the United States with data from RSV seasons (September 1 through April 30) in 2017 through 2020. Participants were children younger than 5 years with medically attended ARI.

Exposure:

For the nirsevimab effectiveness analyses, nirsevimab receipt among infants younger than 8 months as of or born after October 1, 2023.

Main Outcome And Measure:

Medically attended RSV-associated ARI.

Results:

Overall, 28 689 children younger than 5 years with medically attended ARI were enrolled, including 9536 during September 1, 2023, through April 30, 2024, and 19 153 during the same calendar period of 2017-2020. Of these children, 16 196 (57%) were male, and 12 444 (43.4) were female; the median (IQR) age was 15 (6-29) months. During 2023-2024, the proportion of children with RSV was 23% (2199/9490) among all medically attended episodes, similar to 2017-2020. RSV-associated hospitalization rates in 2023-2024 were similar to average 2017-2020 seasonal rates with 5.0 (95% CI, 4.6-5.3) per 1000 among children younger than 5 years; the highest rates were among children aged 0 to 2 months (26.6; 95% CI, 23.0-30.2). Low maternal RSV vaccine uptake precluded assessment of effectiveness. Overall, 10 of 765 case patients (1%) who were RSV positive and 126 of 851 control patients (15%) who were RSV negative received nirsevimab. Nirsevimab effectiveness was 89% (95% CI, 79%-94%) against medically attended RSV-associated ARI and 93% (95% CI, 82%-97%) against RSV-associated hospitalization. Among 229 sequenced specimens, there were no differences in nirsevimab binding site mutations by infant nirsevimab receipt status.

Conclusions And Relevance:

This analysis documented the continued high burden of medically attended RSV-associated ARI among young children in the US. There is a potential for substantial public health impact with increased and equitable prevention product coverage in future seasons.

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