Impact of a community-led intervention on the uptake of childhood vaccines in Liverpool: a protocol for a synthetic control evaluation.

introductionVaccines are our best defence against infectious diseases, yet uptake of childhood immunisation programmes has consistently declined in the UK, with growing concerns around socioeconomic inequalities. Liverpool, in particular, demonstrated some of the lowest uptake rates in England since 2019. In response, the Health Equity Liverpool Project (HELP) implemented a hyper-localised community-led initiative between September 2023 and June 2024 to tackle vaccine hesitancy. Activities included outreach events and school-based engagement across nine sites within Liverpool. Despite promising qualitative evidence, the intervention's impact on childhood vaccine uptake has not yet been quantified. We aim to evaluate the population level impact of the HELP intervention on the uptake of five childhood vaccines (first and second doses of the measles, mumps and rubella vaccine (MMR1, MMR2), 6-in-1 vaccine (diphtheria, tetanus, pertussis, polio, haemophilus influenzae type b and hepatitis B), pneumococcal conjugate vaccine booster dose (PCV) and rotavirus vaccine) using synthetic control methods. METHODS AND ANALYSIS: We will analyse publicly available quarterly vaccine uptake data (between April 2019 and March 2025) from the Cover of Vaccination Evaluated Rapidly programme for general practices (GPs) in England. The intervention group will be defined as practices located within a 1 km radius of the intervention sites. A synthetic control group will be constructed using non-intervention GPs matched on pre-intervention vaccine uptake, and linked demographic, socioeconomic and healthcare capacity covariates. Primary outcomes are the uptake of MMR1 and MMR2 vaccines. Secondary outcomes include the uptake of 6-in-1, PCV and rotavirus vaccines. Average treatment effects will be estimated as the post-intervention difference in uptake between intervention and synthetic control groups. Sensitivity analyses will examine spillover effects, alternative spatial definitions of exposure, the biasing effect of concurrent interventions and the feasibility of analysis at small area neighbourhood level. ETHICS AND DISSEMINATION: This study will be conducted as part of the ReCITE project, which has received ethical approval from the Liverpool School of Tropical Medicine Research Ethics Committee (Reference: 24-018) and is funded by the UK Arts and Humanities Research Council (Project Number: AH/Z505341/1). Findings will be shared with the project funder and submitted for publication in a peer-reviewed journal.