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Global Percentage of Asymptomatic SARS-CoV-2 Infections Among the Tested Population and Individuals With Confirmed COVID-19 DiagnosisA Systematic Review and Meta-analysis

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Question  What is the percentage of asymptomatic individuals with positive test results for SARS-CoV-2 among tested individuals and those with confirmed COVID-19 diagnosis?

Findings  In this systematic review and meta-analysis of 95 unique studies with 29 776 306 individuals undergoing testing, the pooled percentage of asymptomatic infections was 0.25% among the tested population and 40.50% among the population with confirmed COVID-19.

Meaning  The high percentage of asymptomatic infections from this study highlights the potential transmission risk of asymptomatic infections in communities.


Importance  Asymptomatic infections are potential sources of transmission for COVID-19.

Objective  To evaluate the percentage of asymptomatic infections among individuals undergoing testing (tested population) and those with confirmed COVID-19 (confirmed population).

Data Sources  PubMed, EMBASE, and ScienceDirect were searched on February 4, 2021.

Study Selection  Cross-sectional studies, cohort studies, case series studies, and case series on transmission reporting the number of asymptomatic infections among the tested and confirmed COVID-19 populations that were published in Chinese or English were included.

Data Extraction and Synthesis  This meta-analysis was conducted following the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guideline. Random-effects models were used to estimate the pooled percentage and its 95% CI. Three researchers performed the data extraction independently.

Main Outcomes and Measures  The percentage of asymptomatic infections among the tested and confirmed populations.

Results  Ninety-five unique eligible studies were included, covering 29 776 306 individuals undergoing testing. The pooled percentage of asymptomatic infections among the tested population was 0.25% (95% CI, 0.23%-0.27%), which was higher in nursing home residents or staff (4.52% [95% CI, 4.15%-4.89%]), air or cruise travelers (2.02% [95% CI, 1.66%-2.38%]), and pregnant women (2.34% [95% CI, 1.89%-2.78%]). The pooled percentage of asymptomatic infections among the confirmed population was 40.50% (95% CI, 33.50%-47.50%), which was higher in pregnant women (54.11% [95% CI, 39.16%-69.05%]), air or cruise travelers (52.91% [95% CI, 36.08%-69.73%]), and nursing home residents or staff (47.53% [95% CI, 36.36%-58.70%]).

Conclusions and Relevance  In this meta-analysis of the percentage of asymptomatic SARS-CoV-2 infections among populations tested for and with confirmed COVID-19, the pooled percentage of asymptomatic infections was 0.25% among the tested population and 40.50% among the confirmed population. The high percentage of asymptomatic infections highlights the potential transmission risk of asymptomatic infections in communities.

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Article Information

Accepted for Publication: October 8, 2021.

Published: December 14, 2021. doi:10.1001/jamanetworkopen.2021.37257

Open Access: This is an open access article distributed under the terms of the CC-BY License. © 2021 Ma Q et al. JAMA Network Open.

Corresponding Author: Min Liu, PhD, Department of Epidemiology and Biostatistics, School of Public Health, Peking University, 38 Xueyuan Rd, Haidian District, Beijing 100191, China (

Author Contributions: Dr M. Liu had full access to all the data in the study and takes responsibility for the integrity of the data and the accuracy of the data analysis. Drs Ma and J. Liu contributed equally to this study and are co–first authors.

Concept and design: Ma, J. Liu, Jing, M. Liu.

Acquisition, analysis, or interpretation of data: Ma, Q. Liu, Kang, R. Liu, Wu, M. Liu.

Drafting of the manuscript: Ma, Q. Liu, Kang, R. Liu.

Critical revision of the manuscript for important intellectual content: J. Liu, Jing, Wu, M. Liu.

Statistical analysis: Ma, J. Liu, Q. Liu, Jing.

Obtained funding: J. Liu, M. Liu.

Supervision: M. Liu.

Conflict of Interest Disclosures: None reported.

Funding/Support: This work was supported by grants 71934002, 71874003, and 72122001 from the National Natural Science Foundation of China.

Role of the Funder/Sponsor: The sponsor had no role in the design and conduct of the study; collection, management, analysis, and interpretation of the data; preparation, review, or approval of the manuscript; and decision to submit the manuscript for publication.

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