Effectiveness of the CoronaVac vaccine in the elderly population during a Gamma variant-associated epidemic of COVID-19 in Brazil: A test-negative case-control study
Authors: Ranzani Otavio T. , Hitchings Matt D.T. , Dorion Murilo , D’Agostini Tatiana Lang , Cardoso de Paula Regiane , Pereira de Paula Olivia Ferreira , Faria de Moura Villela Edlaine , Scaramuzzini Torres Mario Sergio , Barbosa de Oliveira Silvano , Schulz Wade , Almiron Maria , Said Rodrigo , Dias de Oliveira Roberto , Vieira da Silva Patricia , Navegantes de Araújo Wildo , Gorinchteyn Jean Carlo , Andrews Jason R. , Cummings Derek A.T. , Ko Albert I. , Croda Julio 
Published: May 2021

ABSTRACTObjectiveTo estimate the effectiveness of the inactivated whole-virus vaccine, CoronaVac, against symptomatic COVID-19 in the elderly population of São Paulo State, Brazil during widespread circulation of the Gamma variant.DesignTest negative case-control study.SettingHealth-care facilities in São Paulo State, Brazil.Participants43,774 adults aged 70 years or older who were residents of São Paulo State and underwent SARS-CoV-2 RT-PCR testing from January 17 to April 29, 2021. 26,433 cases with symptomatic COVID-19 and 17,622 symptomatic, test negative controls were selected into 7,950 matched pairs, according to age, sex, self-reported race, municipality of residence, prior COVID-19 status and date of RT-PCR testing.InterventionVaccination with a two-dose regimen of CoronaVac.Main outcome measuresRT-PCR confirmed symptomatic COVID-19 and COVID-19 associated hospitalizations and deaths.ResultsAdjusted vaccine effectiveness against symptomatic COVID-19 was 18.2% (95% CI, 0.0 to 33.2) in the period 0-13 days after the second dose and 41.6% (95% CI, 26.9 to 53.3) in the period ≥14 days after the second dose. Adjusted vaccine effectiveness against hospitalisations was 59.0% (95% CI, 44.2 to 69.8) and against deaths was 71.4% (95% CI, 53.7 to 82.3) in the period ≥14 days after the second dose. Vaccine effectiveness ≥14 days after the second dose declined with increasing age for the three outcomes, and among individuals aged 70-74 years it was 61.8% (95% CI, 34.8 to 77.7) against symptomatic disease, 80.1% (95% CI, 55.7 to 91.0) against hospitalisations and 86.0% (95% CI, 50.4 to 96.1) against deaths.ConclusionsVaccination with CoronaVac was associated with a reduction in symptomatic COVID-19, hospitalisations and deaths in adults aged 70 years or older in a setting with extensive Gamma variant transmission. However, significant protection was not observed until completion of the two-dose regimen, and vaccine effectiveness declined with increasing age amongst this elderly population.Summary boxesWhat is already known on this topicRandomised controlled trials (RCT) have yielded varying estimates (51 to 84%) for the effectiveness of the inactivated whole-virus vaccine, CoronaVac, against symptomatic COVID-19.Current evidence is limited on whether CoronaVac is effective against severe disease or death caused by the SARS-CoV-2 variant of concern, Gamma, or in the setting of extensive Gamma variant circulation.More evidence is needed for the real-world effectiveness of CoronaVac and other inactivated vaccines among elderly individuals, a population that was underrepresented in RCTs of these vaccines.What this study addsA two-dose regimen of CoronaVac provides significant protection against symptomatic COVID-19, hospitalisations and deaths among adults ≥70 years of age in the setting of widespread Gamma variant transmission.Significant protection did not occur until ≥14 days after administration of the second dose of CoronaVac.The effectiveness of CoronaVac declines with increasing age in the elderly population.