Revista de Saúde Pública (Dec 2020)

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

  • Antônio Augusto Moura da Silva,
  • Lídio Gonçalves Lima-Neto,
  • Conceição de Maria Pedrozo e Silva de Azevedo,
  • Léa Márcia Melo da Costa,
  • Maylla Luanna Barbosa Martins Bragança,
  • Allan Kardec Duailibe Barros Filho,
  • Bernardo Bastos Wittlin,
  • Bruno Feres de Souza,
  • Bruno Luciano Carneiro Alves de Oliveira,
  • Carolina Abreu de Carvalho,
  • Erika Barbara Abreu Fonseca Thomaz,
  • Eudes Alves Simões-Neto,
  • Jamesson Ferreira Leite Júnior,
  • Lécia Maria Sousa Santos Cosme,
  • Marcos Adriano Garcia Campos,
  • Rejane Christine de Sousa Queiroz,
  • Sérgio Souza Costa,
  • Vitória Abreu de Carvalho,
  • Vanda Maria Ferreira Simões,
  • Maria Teresa Seabra Soares de Brito e Alves,
  • Alcione Miranda dos Santos

DOI
https://doi.org/10.11606/s1518-8787.2020054003278
Journal volume & issue
Vol. 54

Abstract

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ABSTRACT 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.

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