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Inferring the true number of SARS-CoV-2 infections in Japan

Lauren McKenzie1, Affan Shoukat2, Kai On Wong1

  • 1BlueDot, Toronto, Ontario, Canada.

Journal of Infection and Chemotherapy : Official Journal of the Japan Society of Chemotherapy
|August 12, 2022
PubMed
Abstract

Insights

More than 3 million COVID-19 infections occurred in Japan by December 2021, significantly underreported. This study used statistical modeling to estimate the true infection burden, revealing substantial underascertainment.

Area of Science:

  • Epidemiology
  • Biostatistics
  • Public Health

Background:

  • Over 1.73 million COVID-19 cases were reported in Japan by December 31, 2021.
  • Actual infections were likely underestimated due to mild/subclinical cases and limited early testing.
  • The study focuses on the period from January 16, 2020, to December 31, 2021.

Purpose of the Study:

  • To infer the true number of COVID-19 infections in Japan.
  • To provide a more realistic assessment of the COVID-19 burden.
  • To inform public health control and surveillance measures.

Main Methods:

  • Statistical modeling framework combining reported cases and fatalities.
  • Imputation of true infections using reported deaths and age-specific infection fatality ratios (IFR).
  • IFR estimates adjusted for interventions, vaccination, and variants, with uncertainty accounted for.

Main Results:

  • An estimated 3.07 million (CrI: 2.05-4.24 million) infections by December 31, 2021.
  • This represents 1.77 times the number of reported cases.
  • Findings align with intermittent seroprevalence studies in Japan.

Conclusions:

  • A substantial number of COVID-19 infections in Japan remained unreported, especially in adults.
  • The study offers a more accurate understanding of the true COVID-19 burden.
  • Results can enhance population health control and surveillance strategies.
Keywords:
Case countsInfection fatality ratesSARS-CoV-2Under-ascertainment

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