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Effectiveness of CoronaVac in the setting of high SARS-CoV-2 P.1 variant transmission in Brazil: A test-negative case-control study
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Abstract
Background
Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) variant P.1 emerged in the city of Manaus in late 2020 during a large resurgence of coronavirus disease (COVID-19), and has spread throughout Brazil. The effectiveness of vaccines in settings with widespread P.1 transmission has not been reported.
Methods
We performed a matched test-negative case-control study to estimate the effectiveness of an inactivated vaccine, CoronaVac, in healthcare workers (HCWs) in Manaus, where P.1 accounted for 75% of genotyped SARS-CoV-2 samples at the peak of its epidemic. Information from electronic surveillance databases was used to select cases of RT-PCR-confirmed SARS-CoV-2 infection and matched test-negative controls from 19 January, 2021 to 25 March, 2021. We used conditional logistic regression to estimate the effectiveness in reducing the odds of primary and secondary outcomes of, respectively, symptomatic and any SARS-CoV-2 infection.
Findings
Among 53,176 HCWs, 46,884 (88%) received at least one dose of CoronaVac and 2,656 (5%) underwent RT-PCR testing from 19 January, 2021 to 25 March, 2021. Of 2,797 RT-PCR tests, 776 (28%) were positive. 393 and 135 case-control pairs with and without, respectively, symptomatic illness were selected for the matched analyses. Vaccination with at least one dose was associated with a 0.50-fold reduction (adjusted vaccine effectiveness, 49.6%; 95% CI, 11.3 - 71.4) in the odds of symptomatic SARS-CoV-2 infection during the period 14 days or more after receiving the first dose. Estimated vaccine effectiveness of at least one dose against any SARS-CoV-2 infection was 35.1% (95% CI, −6.6 - 60.5) in the same time period.