SynthesisBMJ open2021
Ratio of asymptomatic COVID-19 cases among ascertained SARS-CoV-2 infections in different regions and population groups in 2020: a systematic review and meta-analysis including 130 123 infections from 241 studies.
Synthesis in BMJ open, 2021. The graph could read no effect estimate from its abstract, so it casts no vote on the map. Cited by 30 papers, 1 of them a synthesis that pooled it.
What it found
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The abstract states no effect estimate the extractor could read, or names no intervention and outcome on the map, so this paper lights no cell and moves no belief. It is still indexed, cited and linked below.
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Trials whose registry record cites this paper, or whose number appears in the abstract. A trial that started after this paper was published is citing it as background, not reporting it.
Neither the registry nor the abstract names a trial number. If this is a trial report, that itself is worth knowing.
Who cites it
30 citing papers in PubMed, 1 synthesis or guideline pooled it.
- Occurrence and transmission potential of asymptomatic and presymptomatic SARS-CoV-2 infections: Update of a living systematic review and meta-analysis.PLoS medicine · 2022Pooled it
- Life Course Malaria Exposure and SARS-CoV-2 Seroepidemiology in Ugandan Adolescents: A Longitudinal Study Nested in a Birth Cohort.Tropical medicine & international health : TM & IH · 2026Article
- SARS CoV-2 seroprevalence and rising antibody titres across successive pandemic waves in accra, Ghana: August 2020 to January 2022.Scientific reports · 2026Article
- Anti-SARS-CoV-2 Antibodies in Urine of Individuals Vaccinated with Janssen AD26.COV2.S COVID-19 Vaccine.Pathogens (Basel, Switzerland) · 2025Article
- Could hybrid work schedules offer infection risk reductions? Insights from a COBuilding and environment · 2025Article
- Longitudinal humoral immunity against SARS-CoV-2 Spike following infection in individuals from Cameroon.Virology · 2025Article
- Age- and vaccination status-dependent isolation guidelines based on simulation of SARS-CoV-2 Delta cases in Singapore.Communications medicine · 2025Article
- The burden of COVID-19 in primary care of Almaty, Kazakhstan, 2021-2022.Scientific reports · 2025Article
- SARS-CoV-2 Prevalence in a Delivering Refugee Population: Refugee Status, Payor Type, Race, and Vaccination Status.Journal of immigrant and minority health · 2025Article
- Factors influencing the rollout and uptake of COVID-19 rapid diagnostic testing: qualitative insights from six African nations.Frontiers in public health · 2025Article
- High SARS-CoV-2 incidence and asymptomatic fraction during Delta and Omicron BA.1 waves in The Gambia.Nature communications · 2024Article
- Silent battles: immune responses in asymptomatic SARS-CoV-2 infection.Cellular & molecular immunology · 2024Review
- PCR testing of traced contacts for SARS-CoV-2 in England, January to July 2021.Euro surveillance : bulletin Europeen sur les maladies transmissibles = European communicable disease bulletin · 2023Article
- Severity of SARS-CoV-2 infection in a hospital population: a clinical comparison across age groups.Italian journal of pediatrics · 2023Article
- Evaluation of the Global Health Security Index as a predictor of COVID-19 excess mortality standardised for under-reporting and age structure.BMJ global health · 2023Article
- Assessing the Impact of Vaccination on the Dynamics of COVID-19 in Africa: A Mathematical Modeling Study.Vaccines · 2023Article
- Effectiveness of BNT162b2 Vaccine against Omicron Variant Infection among Children 5-11 Years of Age, Israel.Emerging infectious diseases · 2023Article
- Clinical evaluation of DIAGNOVIR SARS-CoV-2 ultra-rapid antigen test performance compared to PCR-based testing.Scientific reports · 2023Article
- Rationale for combined therapies in severe-to-critical COVID-19 patients.Frontiers in immunology · 2023Review
- Infection with SARS-CoV-2 variant Gamma (P.1) in Chile increased ICU admission risk three to five-fold.PloS one · 2023Article
Corrections and comments
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Authors and funding
8 authors.
Funding
No grant is acknowledged in the PubMed record.
Abstract
introductionAsymptomatic infection of SARS-CoV-2 may lead to silent community transmission and compromise the COVID-19 pandemic control measures. We aimed to estimate the rate of asymptomatic COVID-19 from published studies and compare this rate among different regions and patient groups.
methodsIn this systematic review and meta-analysis, electronic databases including Medline, Embase, PubMed and three Chinese electronic databases (Chinese National Knowledge Infrastructure [CNKI], WanFang Data and China Science, and Technology Journal Database [VIP]) were searched for literature published from 1 November 2019 to 31 December 2020. Original investigations with sample size (or number of subjects) not less than five were included for further analyses. Subgroup analyses were conducted according to different study types, study periods, geographical regions and patient demographics. The STATA (V.14.0) command 'metaprop' was implemented to conduct a meta-analysis of the pooled rate estimates of asymptomatic infections with exact binomial and score test-based 95% confidence interval (CI).
resultsA total of 130 123 ascertained COVID-19 infections from 241 studies were included in this meta-analysis, including 31 411 asymptomatic infections. The overall rate of asymptomatic infections was 23.6% (18.5%-29.1%) and 21.7% (16.8%-27.0%) before and after excluding presymptomatic cases, respectively. Subgroup analysis showed that significantly higher in pregnant women (48.8%, 28.9%-68.9%), children (32.1%, 24.2%-40.5%), and studies reporting screening programmes (36.0%, 24.6%-48.1%) conducted on or after 1 March 2020 (42.5%, 33.4%-51.9%). In terms of geographical region, the rate was the highest in Africa (64.3%, 56.7%-71.6%), followed by America (40.0%, 27.4%-53.3%), Europe (28.1%, 19.0%-38.1%) and Asia (18.1%, 13.2%-23.5%).
conclusionWe approximated that one-fifth of COVID-19 infections are asymptomatic throughout the course of infection. Public health policies targeting these high-risk groups may be recommended to achieve early identification and more stringent containment of the pandemic.
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