Impact of Nirsevimab on Respiratory Syncytial Virus PCR Test Positivity in Young Infants: A Community‐Level Observational Study in Queensland, Australia

AIM In April 2024 nirsevimab, a long-acting respiratory syncytial virus (RSV)-specific monoclonal antibody, was made available free of charge to all newborn infants in Queensland. We aimed to explore the community-level impact of a nirsevimab-based prevention program on RSV detection percentages among infants aged ≤ 3 months in Queensland, Australia.

METHODS A retrospective analysis of January 2022-December 2024 laboratory data from a Queensland network. Weekly percentages of RSV-positive tests among infants aged ≤ 3 months (eligible group for nirsevimab) were compared with children aged 24-35 months (ineligible group) after nirsevimab introduction in mid-April 2024, and with comparable age data from 2022 to 2023.

RESULTS Overall, 20 956 RSV polymerase chain reaction tests for both age groups were performed during the study period (2022: 5593; 2023: 4910; 2024: 10 453). Following nirsevimab introduction, the percentage of RSV positive tests declined from 16.0% (370/2316) to 5.8% (51/876) among eligible infants (aged ≤ 3 months), compared to 18.6% (1879/10 098) to 14.6% (1117/7666) among ineligible children (aged 24-35 months). Difference-in-differences analysis showed an absolute risk difference of -6.9 percentage points (95% confidence interval: -13.2 to -4.1, p = 0.03).

CONCLUSIONS We present the first real-world community-based evidence on the impact of nirsevimab upon RSV detection percentages in infants aged ≤ 3 months in Queensland, Australia. The nirsevimab-based prevention program may be contributing to a substantial decline in RSV detection percentages among young infants in the community.