COVID-19 Crisis in Brazil: Post-Vaccination Seroprevalence and Infection in More and Less Vaccinated Municipalities in a Northeastern State.

Abstract

Given the impact of the pandemic in Brazil, vaccination is essential to prevent illness and death. Thus, this study sought to compare, after vaccination, the circulation of SARS-CoV-2 and the response to vaccination in the least and most vaccinated municipalities of a Brazilian state during the height of the pandemic when the Omicron variant was dominant. We tested for the SARS-CoV-2 antigen and confirmed infection using an RT-qPCR and measured IgM and IgG antibodies in fully vaccinated participants from municipalities with higher and lower vaccination rates. We showed that participants from the least vaccinated municipalities were more likely to have detectable IgM antibodies and a positive antigen/RT-qPCR result for SARS-CoV-2 than participants from the most vaccinated municipalities. There were no differences between the vaccines used (BNT162b2, Ad26.COV2.S, AZD1222, and CoronaVac) and antibody production. Our study evaluated municipal vaccination coverage and its effects on mortality, infections, and anti-SARS-CoV-2 antibodies during a critical phase of the pandemic. The results suggest that higher vaccination coverage reduces acute cases and confers higher memory antibody levels against SARS-CoV-2. Even with a full vaccination schedule, individuals living in places with low vaccination rates are more susceptible to infection.