High Number of Asymptomatic SARS-CoV-2 Infection During School Reopening in Brazilian Cities

Background: Brazil experienced one of the highest numbers of cases and deaths due to COVID-19. Children and adolescents were increasingly affected in the last waves of the pandemic. Notably, Brazil experienced one of the longest periods of school closures and reopening could have exposed students to high rates of SARS-CoV-2 infection. However, it is still unknown what the infection status of students and school workers was at the time of reopening schools in Brazilian cities. Methods: Here we evaluated viral carriage by RT-PCR and seroprevalence of anti-SARS-CoV-2 antibodies (IgM and IgG) by immunochromatography in 2,259 individuals (1,139 students and 1120 school workers) from schools in 28 Brazilian cities. The study was performed from November 17 th to December 21 st , 2020, during public schools reopening, when classes were conducted in hybrid mode before the start of vaccination campaigns. Findings: Most students (n=421) and school workers (n=446) had active (qRT-PCR+ IgM- IgG- or qRT-PCR+ IgM+ IgG-/+) SARS-CoV-2 infection. Regression analysis indicated a strong association between the infection status of students and school workers. Furthermore, while 45% (n = 515) of the students and 37% (n = 415) of the school workers were neitherantigen nor antibody positive in laboratory tests, 16% of the participants (169 students and 193 school workers) were oligosymptomatic, including those reinfected, presenting mild symptoms such as headache, sore throat, and cough. Notably, most of the individuals were asymptomatic (83.9%) during schools reopening. Interpretation: These results indicate a high number of asymptomatic SARS-CoV-2 infections during school reopening in multiple Brazilian cities. Considering the potential transmission risk of asymptomatic infections in educational settings, preventive (e.g., vaccination) measures will be essential to reduce viral transmission during school reopening in future pandemics. Funding: This study was supported by the Public Ministry of Labor, Federal Public Ministry, and State Public Ministry (grant 06.20.01.0078) and also by the São Paulo Research Foundation (FAPESP grants 2018/18886-9, 2020/01688-0, and 2020/07069-0 to OCM;grant 2020/09146-1 to PPF;2020/16246-2 grant to DLMF) and the coordination for the improvement of higher education personnel–Brazil (CAPES)–finance code 001 granted to I.S.F.