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 50.39% (95% confidence interval [CI], 35.26% to 61.98%; 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⸱58% [95% CI, 34.89% to 52.83%; p= 0.0023] in preventing COVID-19 and 82⸱14% (95% CI, 64.93% to 90.90%; 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.

The authors have declared no competing interest.

NCT0445659

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7558252/

PATH participation (CG) was enabled under a grant (INV-023725) from the Bill & Melinda Gates Foundation.

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The protocol and its three amendments were reviewed and approved by the local Ethics Review Board (Universidade de Sao Paulo Ethics Commitee Board), the Brazilian National Research Ethics Council (CONEP), and ANVISA.

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