The goal of this observational study is to is to examine the impact of new RSV prevention medicines on the burden of RSV disease among young children. The main question it aims to answer is:

What was the impact of the 2025 RSV prevention program on RSV-related hospitalisation in children under 2 years of age?

Participants won't need to do anything additional for the study as only routinely collected health information will be used to answer the research question.

Nirsevimab, a novel long-acting monoclonal antibody targeted at RSV became available for vulnerable babies in the Australian Capital Territory (a small jurisdiction in Australia) in April 2024. Maternal RSV vaccine, Abrysvo, became available for all women of 28-36 weeks gestation in February 2025. Through either nirsevimab or Abrysvo, all infants born from 1 January 2025 in the jurisdiction have universal eligibility for RSV immunoprophylaxis.

This study will use interrupted time series methodology to evaluate the impact of the 2025 RSV prevention program on RSV-related hospitalisation in children under 2 years of age. Historical data from 2022-2023 will form the pre-nirsevimab period, and 2022-2024 the pre-Abrysvo period. 2025 will form the post-intervention period.

Secondary objectives are to:

1. Evaluate the impact of the 2025 RSV prevention program on RSV-related Emergency Department (ED) presentations
2. Evaluate the impact on the reported incidence of RSV

Inclusion Criteria:

• child aged under 2 years
• laboratory confirmed RSV

Exclusion Criteria:

• n/a

The study is set in the Australian Capital Territory, a small Australian jurisdiction with a single acute paediatric service provider.

Deidentified IPD that underlie any published results may be shared upon reasonable request, and subject to ethics and governance processes.

From 3 months after publication of results to 3 years.

Researchers with a methodologically sound proposal, subject to ethics and governance processes. A data sharing agreement will be required.