Effectiveness of the CoronaVac vaccine in older adults during a gamma variant associated epidemic of covid-19 in Brazil: test negative case-control study
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Abstract
Objective
To estimate the effectiveness of the inactivated whole virus vaccine, CoronaVac (Sinovac Biotech), against symptomatic covid-19 in the elderly population of São Paulo state, Brazil during widespread circulation of the gamma variant.
Design
Test negative case-control study.
Setting
Community testing for covid-19 in São Paulo state, Brazil.
Participants
43 774 adults aged ≥70 years who were residents of São Paulo state and underwent reverse transcription polymerase chain reaction (RT-PCR) testing for SARS-CoV-2 from 17 January to 29 April 2021. 26 433 cases with symptomatic covid-19 and 17 622 test negative controls with covid-19 symptoms were formed into 13 283 matched sets, one case with to up to five controls, according to age, sex, self-reported race, municipality of residence, previous covid-19 status, and date of RT-PCR test (±3 days).
Intervention
Vaccination with a two dose regimen of CoronaVac.
Main outcome measures
RT-PCR confirmed symptomatic covid-19 and associated hospital admissions and deaths.
Results
Adjusted vaccine effectiveness against symptomatic covid-19 was 24.7% (95% confidence interval 14.7% to 33.4%) at 0-13 days and 46.8% (38.7% to 53.8%) at ≥14 days after the second dose. Adjusted vaccine effectiveness against hospital admissions was 55.5% (46.5% to 62.9%) and against deaths was 61.2% (48.9% to 70.5%) at ≥14 days after the second dose. Vaccine effectiveness ≥14 days after the second dose was highest for the youngest age group (70-74 years)—59.0% (43.7% to 70.2%) against symptomatic disease, 77.6% (62.5% to 86.7%) against hospital admissions, and 83.9% (59.2% to 93.7%) against deaths—and declined with increasing age.
Conclusions
Vaccination with CoronaVac was associated with a reduction in symptomatic covid-19, hospital admissions, and deaths in adults aged ≥70 years in a setting with extensive transmission of the gamma variant. Vaccine protection was, however, low until completion of the two dose regimen, and vaccine effectiveness was observe to decline with increasing age among this elderly population.
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SciScore for 10.1101/2021.05.19.21257472: (What is this?)
Please note, not all rigor criteria are appropriate for all manuscripts.
Table 1: Rigor
Ethics IRB: The study was approved by the Ethical Committee for Research of Federal University of Mato Grosso do Sul (CAAE: 43289221.5.0000.0021).
Field Sample Permit: The work of investigators at the University of Florida, Yale University, Stanford University, and Barcelona Institute for Global Health was conducted to inform the public health response and was therefore covered under Public Health Response Authorization under the US Common Rule.Sex as a biological variable not detected. Randomization not detected. Blinding not detected. Power Analysis Power calculation: After generating matched case-control pairs and before performing the analyses, we simulated the power of the data set to identify a … SciScore for 10.1101/2021.05.19.21257472: (What is this?)
Please note, not all rigor criteria are appropriate for all manuscripts.
Table 1: Rigor
Ethics IRB: The study was approved by the Ethical Committee for Research of Federal University of Mato Grosso do Sul (CAAE: 43289221.5.0000.0021).
Field Sample Permit: The work of investigators at the University of Florida, Yale University, Stanford University, and Barcelona Institute for Global Health was conducted to inform the public health response and was therefore covered under Public Health Response Authorization under the US Common Rule.Sex as a biological variable not detected. Randomization not detected. Blinding not detected. Power Analysis Power calculation: After generating matched case-control pairs and before performing the analyses, we simulated the power of the data set to identify a vaccine efficacy of 40% comparing those with two doses ≥14 days after the second dose to those who had not received a vaccine (see the protocol for details). Table 2: Resources
No key resources detected.
Results from OddPub: Thank you for sharing your code and data.
Results from LimitationRecognizer: We detected the following sentences addressing limitations in the study:This study has limitations that should be acknowledged. We evaluated CoronaVac effectiveness against symptomatic disease, but a detailed evaluation of effectiveness with regards to severity, hospitalization and deaths is needed to inform public health planning. A preliminary aggregated analysis using weekly times series of COVID-19 deaths in Brazil showed a relative decrease among those ≥80 years compared with all ages after the vaccination with CoronaVac and ChAdOx1 in the country,27 suggesting a discernible impact of vaccination on the most severe outcomes. We could not evaluate the vaccine effectiveness in those with or without previous infection because of the limited number of previously positive individuals by RT-PCR and rapid antigen tests. Previous COVID-19-like illness was less common in those with positive RT-PCR before matching, showing likely some degree of protection of previous infection. The estimated seroprevalence of COVID-19 in the São Paulo State capital (∼12million) in those ≥60 years was 19.9% (95% CI, 14.9-29.9) in January 2021 before vaccination.28 Finally, as this is an observational study, there is likely unmeasured confounding. The “bias-indicator” association between recent vaccination with a single dose 0-13 days before sample collection was close to null, suggesting that vaccinated and unvaccinated individuals did not differ greatly in their underlying risk of testing positive for SARS-CoV-2, independently of vaccination.12,14 However, this does n...
Results from TrialIdentifier: No clinical trial numbers were referenced.
Results from Barzooka: We did not find any issues relating to the usage of bar graphs.
Results from JetFighter: We did not find any issues relating to colormaps.
Results from rtransparent:- Thank you for including a conflict of interest statement. Authors are encouraged to include this statement when submitting to a journal.
- Thank you for including a funding statement. Authors are encouraged to include this statement when submitting to a journal.
- No protocol registration statement was detected.
Results from scite Reference Check: We found no unreliable references.
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