O. Ranzani, M. Hitchings, Murilo Dorion, T. D’agostini, Regiane Cardoso de Paula, Olivia Ferreira Pereira de Paula, E. Faria de Moura Villela, Mario Sergio Scaramuzzini Torres, Silvano Barbosa de Oliveira, W. Schulz, M. Almiron, R. Said, Roberto Dias de Oliveira, Patricia Vieira da Silva, Wildo Navegantes de Araújo, J. C. Gorinchteyn, Jason R. Andrews, D. Cummings, A. Ko, J. Croda
medRxiv, 2021
Background Mass vaccination is being used in response to coronavirus disease (COVID-19) epidemics, including those driven by emerging variants of concern. We evaluated the effectiveness of the inactivated whole-virus vaccine, CoronaVac, against symptomatic COVID-19 in the elderly population of Sao Paulo State, Brazil during widespread circulation of the P.1 variant. Methods We conducted a test-negative, case-control study of adults >=70 years of age from Sao Paulo State from January 17 to April 29, 2021, during which vaccination with a two-dose regimen of CoronaVac was implemented. We identified RT-PCR-confirmed COVID-19 cases and controls who had a symptomatic illness with a negative RT-PCR test from national surveillance and state vaccination databases. Controls were pair-matched to cases by age category, sex, race, municipality, prior COVID-19 status, and date of RT-PCR testing. We estimated vaccine effectiveness, adjusted for age and comorbidities, using conditional logistic regression. Findings We selected 7,950 matched pairs with a mean age of 76 years from 26,433 COVID-19 cases and 17,622 test-negative controls. Adjusted vaccine effectiveness was 18.2% (95% CI, 0.0 to 33.2) and 41.6% (95% CI, 26.9 to 53.3) in the period 0-13 and >=14 days, respectively, after the 2nd dose. Administration of a single vaccine dose was not associated with reduced odds of COVID-19. Vaccine effectiveness >=14 days after the 2nd dose declined with increasing age and was 61.8% (95% CI 34.8 to 77.7), 48.9% (95% CI 23.3 to 66.0) and 28.0% (95% CI 0.6 to 47.9) among individuals 70-74, 75-79 and >=80 years of age, respectively (p-interaction = 0.05). Interpretation CoronaVac was 42% effective in the real-world setting of extensive P.1 transmission, but significant protection was not observed until completion of the two-dose regimen. These findings underscore the need to maintain non-pharmaceutical interventions when mass vaccination with CoronaVac is used as part of an epidemic response. Funding Pan American Health Organization
Cited by 12 publications.
Field of study: Medicine