Background: Rumors about vaccine failure directly affect the population's risk perceptions, adherence to the vaccine schedule, and health measures to combat the COVID-19 pandemic. Based on the occurrence of these events in a municipality in northern Brazil, the objective was to investigate the suspicion of vaccine failure for severe cases and deaths due to COVID-19 in people with the complete vaccine schedule and the individual characteristics possibly associated with this occurrence.
Methods: The screening method was used to assess vaccine effectiveness in individuals with the complete Sinovac regimen (n=43,777) and those with signs/symptoms of severity or death from 14 days after the 2d dose of the vaccine (probable cases of vaccine failure). Data sources were national information systems. A case-control (1:4) was carried out to assess predisposing factors to disease severity. Cases were probable cases of vaccine failure and controls were individuals with the complete Sinovac regimen and without signs and symptoms of severity or death. Simple random and stratified for age sampling was carry out based on health service records to select the population. Adjusted odds ratio (aOR) and its confidence interval (95% CI) were calculated using logistic regression.
Results: A total of 9 probable cases were identify. Among these, the mean age was 73.1±17.0 years and hypertension was the most frequent comorbidity (5/9). The total vaccine effectiveness was 99.7% and varied between 98.0% (60–64 years old) to 22.4% (85 years old or more). For the case-control, obesity (aOR=9.8; 95% CI=1.2–77.7) remained associated with severity and death by COVID-19.
Conclusions: These findings show the high Sinovac vaccine effectiveness and that, probably, obesity and senescence may have contributed to the severity and death among the cases. The evidence raised by the study helps to combat the rumors and strengthen measures to control the pandemic. It is recommended to encourage immunization campaigns in the state, especially in people with comorbidities.