Protocol to measure COVID-19 XBB.1.5 vaccine effectiveness in the immunocompromised population during the 2023 autumn vaccination campaign
The European Centre for Disease Prevention and Control (ECDC) started several vaccine effectiveness (VE) studies in 2020. These were included in the Vaccine Effectiveness, Burden and Impact Studies (VEBIS) project in 2021 to monitor VE in different settings and using different methods, and to provide information on different outcomes (severe disease, moderate disease, infection, transmission, etc) (1–3).
Within the VEBIS project, the protocol describes the methods to estimate the Coronavirus disease 2019 (COVID-19) XBB.1.5. monovalent-adapted VE in immunocompromised persons (ICP), against COVID-19 hospitalisations and deaths, using established health data registries across six participating European Union/European Economic Area (EU/EEA) countries. The protocol is aimed at implementing a specific question that has been identified as an area where additional scientific evidence is beneficial, in the context of the ECDC/EMA Vaccine Monitoring Platform research agenda (4), adding on the routine vaccine effectiveness monitoring performed across the six countries (5). This work is performed within the VEBIS Lot 4 framework contract.
The study design is a retrospective cohort study using data from ICPs eligible for COVID-19 vaccination at the start of the 2023 autumn vaccination campaign, collected routinely in electronic health record (EHR) databases. The study starts at the beginning of the vaccination campaign for each study site and ends 12 months after that. The study has two outcomes of interest: hospitalisations and deaths due to COVID-19. Data to be collected, besides the outcomes of interest, include sociodemographic (age, sex), clinical (ICP group) and COVID-19 vaccination history (brand, number of doses and dates of prior vaccine dose administration).
The protocol outlines the study design and methods for analysing the data at country level and includes a plan for the pooled analysis across countries. This protocol is primarily intended to guide the implementation of the ECDC-funded studies within the VEBIS project with a focus on specific objectives. Nevertheless, ECDC encourages the conduct of VE studies using this protocol and other VEBIS-related protocols as a basis in countries that do not currently plan to participate in ECDC-funded studies. Consistent protocols will facilitate the comparability of results across studies, countries, and sites.
