Nat Med. last month compared to their counterparts. Among the infected, 26.0% were asymptomatic. The infection fatality rate (IFR) was 0.14%, higher for men and older adults. The IFR based on excess deaths was 0.28%. The ratio of estimated infections to reported cases was 22.2. CONCLUSIONS: Deltarasin HCl To the best of our knowledge, the seroprevalence of SARS-CoV-2 estimated in this population-based survey DCN is one of the highest reported. The local herd immunity threshold may have been reached or might be reached soon. DESCRIPTORS: Seroepidemiologic Studies, Coronavirus Infections, Immunity, Herd, Mortality INTRODUCTION Brazil is one of the countries most severely affected by the coronavirus disease 2019 (COVID-19) pandemic. By September 21, 2020, 4,558,040 cases were reported, with 137,272 deaths 1. The national response has been controversial, testing capacity is low, and disagreements among the different levels of government over social distancing measures conveyed contradictory messages to the population. As a middle-income country, Brazil has high poverty rates and an extensive part of its population is engaged in informal activities that face difficulties to make ends meet and to follow stay-at-home measures 2 . As a consequence of all these facts, social distancing has not reached levels sufficient to curb and contain the COVID-19 pandemic 3 . The state of Maranh?o is located in the Northeast Deltarasin HCl region of Brazil and has a population of 7,114,598 inhabitants in 2020 4 , with an area of 329,642 km2, a little larger than that of Italy. It is one of the states in Brazil, where the pandemic gathered speed early. Its first case was reported on March 20, 2020, and by September 21, 2020 the number of deaths reported was 3,664. Deaths peaked in May and decreased thereafter. From May 3, Deltarasin HCl 2020 to May 17, 2020, S?o Lus Island, where the state capital city is located, was put into lockdown. Reduction of social mobility reached at most 55% at the end of March and during lockdown at the capital, remaining low (40%C45%) during the worst phase of the pandemic. Despite low home quarantine adherence, the number of deaths decreased, and intensive care units occupancy diminished 5 . Herd immunity threshold to attain control of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is an ongoing debate. Although some consider it to be around 60%C70%, using the classical formula 1C1/R0, in which R0 may be the simple reproductive # 6 6 , other reviews have suggested that herd immunity could possibly be only 10%C20% 7 or about 43% 8 , because of the heterogeneity in publicity or susceptibility to an infection across people groupings 7,8 . Nevertheless, reported population-based seroprevalences of SARS-CoV-2 had been less than the herd Deltarasin HCl immunity thresholds, which range from low attacks prices incredibly, near 1%C3% 9,10 , to beliefs up to 14.3% in Barcelona 11 , Spain, and 22.7% in NEW YORK 12 . In Brazil, the best reported population-based seroprevalences had been 17.9%, for the S?o Paulo municipality 13 , and 66% for Manaus, where herd immunity may have performed a significant function in stablishing how big is the epidemic 14 . Chlamydia fatality price (IFR) as well as the percentage of asymptomatic attacks of SARS-CoV-2 are known with doubt. Early reports at the start from the pandemic approximated IFR at beliefs between 0.6% and 1.3% 15,16 , and considered asymptomatic infections to be prevalent 15 highly,17 . Latest reviews, however, approximated a lesser IFR with huge variants across sites 10,18 and a lower percentage of asymptomatic attacks 11,19,20 . Population-based research are essential to monitor chlamydia development, since most situations are undocumented 21 . Nevertheless, few population-based.