CoronaVac shows 50% Effectiveness in a Brazilian Cohort

CoronaVac vaccine from Sinovac is a well-tolerated vaccine containing inactivated SARS-CoV-2. It had induced humoral responses in phase 1 and phase 2 studies. Vaccine efficacy refers to the proportion of reduction in disease among vaccinated individuals in a clinical trial, while vaccine effectiveness is the reduction in disease vaccinated persons in real-world conditions. Studies have not focused on the effectiveness of CoronaVac so far. Researchers from Brazil recently reported the occurrence of symptomatic COVID-19 in a group of healthcare workers vaccinated with CoronaVac.

They also estimated the effectiveness of the vaccine. The study is published on a pre-print server. CoronaVac was given to the study cohort of 22,402 healthcare workers in Hospital das Clinicas during 18 and 21 January 2021 (epi week 3) and 21,652 healthcare workers during 14-16 February 2021 (epi week 7). A total of 380 healthcare workers were diagnosed with COVID-19 since the first dose of the vaccine.

The number of COVID-19 cases in the city increased sharply in 2021, but the number of cases among the healthcare workers did not follow the same trend. The estimated effectiveness of the vaccine 2 and 3 weeks after the 2nd dose was 50.7% and 51.8%, respectively. Effectiveness increased over the next 2 weeks. Forty-seven percent of the samples, or 67 out of 142, had variants of concern, mostly P1.

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