Update to: Study Pre-protocol for "BronchStart - The Impact of the COVID-19 Pandemic on the Timing, Age and Severity of Respiratory Syncytial Virus (RSV) Emergency Presentations; a Multi-Centre Prospective Observational Cohort Study".

Background: In 2021 we launched the BronchStart study, which collected information on 17,899 presentations in children with serious respiratory tract infections following the release of lockdown restrictions. Our study informed the Joint Committee on Vaccination and Immunisation's decision to recommend the introduction maternal respiratory syncytial virus (RSV) vaccination, which was introduced in the United Kingdom in August/September 2024.

Study Question: We modified our original protocol to conduct a United Kingdom-wide assessment of maternal vaccination against RSV.

Methods And Likely Impact: We will conduct a multi-centre study, utilising the PERUKI network used in the original BronchStart study, to assess the effectiveness of maternal vaccination using a test-negative study design. We will gather detailed clinical information on children admitted with bronchiolitis in the post-RSV vaccination era, and understand possible reasons for incomplete vaccine uptake.