Efficacy and Safety of an Inactivated Whole-Virion Sars-Cov-2 Vaccine (Coronavac) in Brazilian Healthcare Professionals: The Profiscov Trial

Background: CoronaVac, an inactivated COVID-19 vaccine, underwent evaluation for its efficacy and safety during the PROFISCOV study conducted in Brazil. Methods: Between July 21, 2020, and July 29, 2021, 13,166 participants provided informed consent, with 12,688 randomized for the trial. Participants were allocated between vaccine and placebo arms (1:1) and monitored for symptomatic COVID-19 cases, severity of disease, and adverse reactions after two doses given 14 days apart. Findings: The primary efficacy analysis revealed a vaccine efficacy of 50⸱4% (95% confidence interval [CI], 35·3% to 62·0%; p=0·0049) in preventing symptomatic COVID-19, leading to the issuance of Emergency Use Authorization for CoronaVac in January 2021. Upon completion of follow-up, vaccine efficacy was 44⸱6% [95% CI, 34·9% to 52·8%; p= 0·0023] in preventing COVID-19 and 82⸱1% (95% CI, 64·9% to 90·9%; p<0·0001) in preventing severe COVID-19. Safety data indicated that adverse reactions were more frequent in the vaccine arm, primarily mild to moderate, with pain at the injection site and headache being the most common. Interpretation: CoronaVac demonstrated moderate efficacy in preventing symptomatic COVID-19 and high efficacy against severe disease. While reactions were slightly more common in the vaccine group, they were generally mild and manageable. Funding: Fundação Butantan, Instituto Butantan, and São Paulo Research Foundation (FAPESP; Grants 2020/10127-1 and 2020/06409-1).