This core protocol for ECDC studies of vaccine effectiveness against hospitalisation with Severe Acute Respiratory Infection laboratory-confirmed with SARS-CoV-2 or with influenza, version 2.0, represents an update to the main elements for a multi-country hospital-based study of COVID-19 vaccine effectiveness in patients hospitalised with Severe Acute Respiratory Infection (SARI), already published as version 1.0.

This protocol presents a common methodology to estimate vaccine effectiveness (VE) for COVID-19, using established health data registries in participating EU/EEA Member States.

This issue of the Communicable Disease Threats Report (CDTR) covers the period 23-29 January 2023 and includes updates on COVID-19, diphtheriae, influenza, chikungunya, dengue and poliomyelitis.