  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.
