The challenges imposed by the COVID-19 pandemic have driven governmental and non-governmental institutions around the world in the search for control, treatment, and prevention measures. Strategies to mitigate pandemic impact include the development of safe and effective vaccines to prevent severe cases and deaths.
In Brazil, the National Health Surveillance Agency approved the emergency use of CoronaVac and AstraZeneca vaccines in January 2021. A few months into the national vaccination campaign however, the deaths of three local health workers who had each received a complete schedule of the CoronaVac vaccine triggered a rumor about vaccine failure in the northern state of Roraima.
Considering the potential impact of this rumor on the population's perceptions of risk, adoption of protective health measures, and adherence to the vaccination campaign, the Brazilian Field Epidemiology Training Program (EpiSUS) was called to provide support to the local health authorities. EpiSUS fellows designed a study to investigate vaccine failure as a potential cause for severe COVID-19 cases and deaths in Roraima residents who were fully vaccinated. Four lines of investigation were initiated, including case series and case-control studies, evaluations of vaccine effectiveness, and possible immunization errors.
Vaccinated individuals who presented with symptoms and signs of severe COVID-19 disease or death at least 14 days after receiving their second dose of the CoronaVac vaccine in the state of Roraima were investigated. Data collection included reviewing databases of the Influenza Epidemiological Surveillance Information System, National Immunization Program, and public and private hospitals. Data was linked across the databases to identify possible cases . Nine probable cases of vaccine failure were identified. These individuals were further described in a case series, which showed that all had pre-existing comorbidities and/or were above 60 years of age. In addition, the researchers found that obesity was a statistically significant risk factor influencing the severity of COVID-19 infection.
Ultimately, EpiSUS fellows found a total vaccine effectiveness rate of 97.74 percent when looking at the number of probable cases of vaccine failure (n=9) as a proportion of the population with a complete vaccination schedule. Fellows also conducted an evaluation of the knowledge and practices of individuals administering vaccines, identifying a number of areas for improvement, including record keeping, screening of patient symptoms before vaccination, and monitoring vaccine temperature during storage. As a result, fellows recommended that local health authorities provide training on immunization best practices to local health professionals including nurses and technicians.
Despite the challenges involved in investigating vaccine-related issues, it was possible to identify that vaccine effectiveness was within the expected parameters, and that individual factors such as obesity and older age may have been related to the negative outcomes. These findings were critical to help fight the rumor, regain trust in the health system, and boost the national immunization campaign.