Coronavirus prevalence in Brazilian Amazon and Sao Paulo city

SARS-CoV-2 spread rapidly in the Brazilian Amazon. Mortality was elevated,
despite the young population, with the health services and cemeteries
overwhelmed. The attack rate in this region is an estimate of the final
epidemic size in an unmitigated epidemic. Here we show that by June, one
month after the epidemic peak in Manaus, capital of the Amazonas state,
44% of the population had detectable IgG antibodies. This equates to a
cumulative incidence of 52% after correcting for the false-negative rate
of the test. Further correcting for the effect of antibody waning we
estimate that the final attack rate was 66%. This is higher than seen in
other settings, but lower than the predicted final size for an unmitigated
epidemic in a homogeneously mixed population. This discrepancy may be
accounted for by population structure as well as some limited physical
distancing and non-pharmaceutical measures adopted in the city.