Enhancing MMR vaccination surveillance in England: Comparing and contrasting new individual-level and existing aggregate data sources

Introduction: Cover of Vaccination Evaluated Rapidly (COVER), ImmForm's early childhood baseline (ImmForm), and the Immunisation Information System (IIS) are data sources used by the UK Health Security Agency (UKHSA) to monitor vaccinations in England. MMR vaccination statistics from these sources are publicly available; however, their concordance is currently unverified. This risks ambiguous and contradictory reporting by national and local health users, which could impact outbreak analysis, interventions, and efforts to reduce vaccination inequalities. This study quantifies the statistical concordance from these sources, provides context around their appropriate use, and validates IIS's newly acquired MMR data. Methods: We compared MMR vaccination records and coverage in those aged 24 and 60 months old. This included stratification by dose, NHS commissioning regions, and financial year quarters between April 2022 and June 2023. IIS and ImmForm vaccination records and coverage were compared against COVER. Results: Across all dose-age cohorts and regions, the median percentage difference in vaccination coverage derived from ImmForm compared to COVER was minimal (≤ 1.10 %) but was substantially different for IIS (≤ 6.90 %). Examining the vaccine (numerator) and eligible individual (denominator) records, IIS had substantially fewer vaccine records than COVER (n = -140,027), which varied regionally. A proportion of this was attributed to missing vaccine records coded solely by Systematised Nomenclature of Medicine product code. Conclusions: Inclusive of its missing vaccine records, IIS will join COVER and ImmForm as a concordant source of MMR vaccination statistics for UKHSA surveillance. Other national and local users should assess whether differences in data source scope, as well as inter-regional and inter-source data discrepancies, impact their use. The continued availability of all sources provides the UKHSA with surveillance flexibility and permits previously impossible cross-validation.