Effectiveness of Inactivated COVID-19 Vaccine of the First Booster Dose

This is a retrospective test-negative case-control study in São Paulo city, Brazil . The COVID-19 Vaccine (CoronaVac® )produced by Sinovac Research and Development Co., Ltd.The main purpose of this study is to measure vaccine effectiveness of homologous booster-dose vaccination with CoronaVac® against laboratory-confirmed symptomatic disease.A total of 14000 subjects will be enrolled,including 7,000 positive cases and 7,000 test negative COVID-19 cases The Statistical Analysis Plan (SAP) will include univariate (and, when required, multivariable) models of logistic regression.Data will be recovered from three health surveillance information electronic health records (EHRs): 1. VACIVIDA, comprising individual data for people vaccinated against SARS-Cov-2. 2. E-SUS, mandatory report database for mild to moderate COVID-19. 3. SIVEP-GRIPE, mandatory report database for severe cases of COVID-19. All those RWD sources are available at the São Paulo Municipality Centers for Health Surveillance.