The Seroconversion History of SARS-CoV-2 in Indigenous People from Brazil – The Interplay between Exposure, Vaccination, and Tuberculosis

Background: The ongoing COVID-19 pandemic caused a significant loss of human lives and a worldwide decline in quality of life. Although our understanding of the pandemic has improved significantly since the beginning, the natural history of COVID-19 and its impacts on under-represented populations, such as Indigenous people from America, remain largely unknown.Methods: We report a retrospective serological survey of two Brazilian Indigenous populations (n=624), Tupiniquim and Guarani-Mbyá. Blood samples were collected between September 2020 and July 2021: a period of eleven (11) months comprising the dissemination of SARS-CoV-2 variants and the beginning of COVID-19 vaccination in Brazil. Seroconversions against SARS-CoV-2 S and N antigens were assessed using three different commercially available ELISA kits. Samples were also used to assess the prevalence of tuberculosis (TB) in the same population (n=529).Findings: We found that 56·0% (n=349/623) of individuals seroconverted for SARS-CoV-2 antigens according to one or more ELISA assays during the period. Relative seroconversion peaked after introduction of the Coronavac (Sinovac) vaccine in February 2021. Vaccination increased the proportion of individuals producing anti-S IgG from 3·9% to 48·6% among ELISA-positive individuals. Our results also indicated that 11·0% (n=46/417) of all individuals were positive for TB. Seroconversion for SARS-CoV-2 was similar between TB-positive versus TB-negative individuals.Interpretation: Most vaccinated individuals seroconverted against SARS-CoV-2 antigens, indicating that Coronavac may be as protective in individuals from Tupiniquim and Guarani-Mbyá groups as observed in the general Brazilian population. COVID-19 severity was minimal regardless of incomplete vaccine coverage, suggesting that vaccination may not be the only factor protecting individuals from severe COVID-19. Tuberculosis is highly prevalent in the population studied and was not associated with increased seroconversion to SARS-CoV-2.Funding: This work was supported by Fapes/CNPq-Pronex (568/2018), FAPESP (2020/05326-5) and FINEP (01.20.0003.00).Declaration of Interest: Authors declare that they have no competing interests.Ethical Approval: The study followed the ethical protocols of the responsible committee on human experimentation and was approved by the ethics committees from the National Research Ethics Committee (CONEP, acronym in Portuguese, no 4599) and the Federal University of Espírito Santo. All the patients signed the consent for inclusion in this study.