Protocol for a COVID-19 vaccine effectiveness multi-country cohort study in the paediatric population aged 5-17 years using electronic health records in EU/EEA countries : recommendations for strengthening preparedness planning

This protocol describes the common methodology to be applied to established health data registries across seven participating European Union/European Economic Area (EU/EEA) Member States to estimate vaccine effectiveness for Coronavirus disease 2019 (COVID-19) in children and adolescents aged 5-17 years old. This work was performed within the Vaccine Effectiveness, Burden and Impact Studies (VEBIS) project [1]. The study design is a retrospective cohort study using data from paediatric populations aged under 18 years old and eligible for COVID-19 vaccination, collected routinely in electronic health records databases. The study started at the beginning of the vaccination campaign for each age cohort and country (5-11 years old, 12-17 years old) and ended one year after. The outcome of interest is hospital admission due to COVID-19. Data collected, besides the outcome of interest, included sociodemographic (age, sex), clinical (comorbidities, previous history of severe acute respiratory syndrome - coronavirus 2 (SARS-CoV-2) infection) and COVID-19 vaccination history (brand, number and dates of dose administration). The protocol outlines the methodology for analysing data at the country level and includes a plan for the pooled analysis. This master protocol was primarily intended to guide the implementation of one study within the VEBIS project. However, ECDC encourages, using this protocol as a basis to conduct vaccine effectiveness studies in countries that do not currently plan to participate in ECDC-funded studies. Consistent protocols will facilitate comparability of results across studies, countries and sites.