Attack rate of COVID-19 and the onset of herd immunity in Manaus, Brazil

Buss et al. (2021) and Faria et al. (2021) reported that ~76% of the residents of the capital city of Manaus, had been infected by SARS-CoV-2 by October 2020 suggesting that herd immunity had been achieved by the end of the first wave. But the announcement of herd immunity, which would imply reasonable protection from future outbreaks, only provided the Manaus population with a false sense of security. Within two months later, a second wave of COVID-19 was initiated with death rates much larger than the first attributed to the appearance of the new P.1 Variant of Concern. Faria et al. (2021) suggest that large scale reinfections played an important role in enabling the huge second epidemic wave. In this Technical Comment we challenge such interpretations, and provide quantitative arguments that suggest the attack rate of the first wave was well below 76%. We then present alternative interpretations of the data.