Trends in the prevalence of COVID-19 infection in Rio Grande do Sul, Brazil: repeated serological surveys. - Hallal PC; Horta BL; Barros AJD; Dellagostin OA; Hartwig FP; Pellanda LC; Struchiner CJ; Burattini MN; Silveira MFD; Menezes AMB; Barros FC; Victora CG (Ciencia & saude coletiva, 2020)