The estimate of the cumulative incidence of SARS-CoV-2 of 76% in Manaus by October 2020 by Buss et al . relies on the assumption of an exponentially-declining probability of sero-reversion over time . We present an alternative, empirically-supported approach that is based on the observed dynamics of antibody titers in sero-positive cases . Through this approach we revise the cumulative incidence estimate to 66% (63.3% - 68.5 %) by October 2020 . This estimate has implications for the proximity to herd immunity and future estimates of fitness advantages of virus variants, such as the P.1 variant of concern . This methodology is also relevant for any other sero-survey analysis that has to adjust for sero-reversion.