Surveillance of COVID-19 vaccine effectiveness – a real-time case-control study in southern Sweden

The extensive register infrastructure available for COVID-19 surveillance in Scania county, Sweden, makes it possible to classify cases with respect to hospitalization and disease severity, stratify on time since last dose and demographic factors, account for prior infection, and extract data for population controls automatically. Estimated vaccine effectiveness 0-3 months after the last dose remained stable during the study period but waned markedly 6 months after the last dose in older persons.