Proportion of asymptomatic coronavirus disease 2019: A systematic review and meta-analysis

J Med Virol. 2021 Feb;93(2):820-830. doi: 10.1002/jmv.26326. Epub 2020 Aug 13.


We aim to systematically review the characteristics of asymptomatic infection in the coronavirus disease 2019 (COVID-19). PubMed and EMBASE were electronically searched to identify original studies containing the rate of asymptomatic infection in COVID-19 patients before 20 May 2020. Then mate-analysis was conducted using R version 3.6.2. A total of 50 155 patients from 41 studies with confirmed COVID-19 were included. The pooled percentage of asymptomatic infection is 15.6% (95% CI, 10.1%-23.0%). Ten included studies contain the number of presymptomatic patients, who were asymptomatic at screening point and developed symptoms during follow-up. The pooled percentage of presymptomatic infection among 180 initially asymptomatic patients is 48.9% (95% CI, 31.6%-66.2%). The pooled proportion of asymptomatic infection among 1152 COVID-19 children from 11 studies is 27.7% (95% CI, 16.4%-42.7%), which is much higher than patients from all aged groups. Abnormal CT features are common in asymptomatic COVID-19 infection. For 36 patients from 4 studies that CT results were available, 15 (41.7%) patients had bilateral involvement and 14 (38.9%) had unilateral involvement in CT results. Reduced white blood cell count, increased lactate dehydrogenase, and increased C-reactive protein were also recorded. About 15.6% of confirmed COVID-19 patients are asymptomatic. Nearly half of the patients with no symptoms at detection time will develop symptoms later. Children are likely to have a higher proportion of asymptomatic infection than adults. Asymptomatic COVID-19 patients could have abnormal laboratory and radiational manifestations, which can be used as screening strategies to identify asymptomatic infection.

Keywords: COVID-19; Coronavirus disease 2019; SARS-CoV-2; asymptomatic infection; children coronavirus disease 2019; presymptomatic infection.

Publication types

  • Meta-Analysis
  • Research Support, Non-U.S. Gov't
  • Systematic Review

MeSH terms

  • Asymptomatic Infections
  • Biomarkers / blood
  • C-Reactive Protein / metabolism*
  • COVID-19 / blood
  • COVID-19 / diagnostic imaging*
  • COVID-19 / epidemiology*
  • COVID-19 / virology
  • China / epidemiology
  • Female
  • Humans
  • L-Lactate Dehydrogenase / blood*
  • Leukocyte Count
  • Male
  • Real-Time Polymerase Chain Reaction
  • SARS-CoV-2 / genetics
  • Tomography, X-Ray Computed


  • Biomarkers
  • C-Reactive Protein
  • L-Lactate Dehydrogenase