Population-based seroprevalence of SARS-CoV-2 and the herd immunity threshold in Maranhão

Rev Saude Publica. 2020 Dec 14:54:131. doi: 10.11606/s1518-8787.2020054003278. eCollection 2020.


Objective: To estimate the seroprevalence of SARS-CoV-2 in the state of Maranhão, Brazil.

Methods: A population-based household survey was performed, from July 27, 2020 to August 8, 2020. The estimates considered clustering, stratification and non-response. Qualitative detection of IgM and IgG antibodies was performed in a fully-automated Elecsys® Anti-SARS-CoV-2 electrochemiluminescence immunoassay on the Cobas® e601 analyzer (Roche Diagnostics).

Results: In total, 3,156 individuals were interviewed. Seroprevalence of total antibodies against SARS-CoV-2 was 40.4% (95%CI 35.6-45.3). Population adherence to non-pharmaceutical interventions was higher at the beginning of the pandemic than in the last month. SARS-CoV-2 infection rates were significantly lower among mask wearers and among those who maintained social and physical distancing in the 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: To the best of our knowledge, the seroprevalence of SARS-CoV-2 estimated in this population-based survey is one of the highest reported. The local herd immunity threshold may have been reached or might be reached soon.

MeSH terms

  • Adolescent
  • Adult
  • Aged
  • Antibodies, Viral / blood*
  • Brazil / epidemiology
  • COVID-19 / immunology*
  • Child
  • Child, Preschool
  • Female
  • Humans
  • Immunity, Herd*
  • Infant
  • Infant, Newborn
  • Male
  • Middle Aged
  • Pandemics
  • SARS-CoV-2
  • Seroepidemiologic Studies*
  • Young Adult


  • Antibodies, Viral

Grants and funding

Secretaria de Saúde do Estado do Maranhão and Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (Capes - finance code 001, Brasil)