SynthesisProceedings of the National Academy of Sciences of the United States of America2021
Asymptomatic SARS-CoV-2 infection: A systematic review and meta-analysis.
Synthesis in Proceedings of the National Academy of Sciences of the United States of America, 2021. The graph could read no effect estimate from its abstract, so it casts no vote on the map. Cited by 272 papers, 6 of them syntheses that pooled it.
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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.
The trial behind it
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
272 citing papers in PubMed, 6 syntheses or guidelines pooled it.
- Impact of disease severity, age, sex, comorbidity, and vaccination on secondary attack rates of SARS-CoV-2: a global systematic review and meta-analysis.BMC infectious diseases · 2025Pooled it
- Pooled it
- Comparative effectiveness of contact tracing interventions in the context of the COVID-19 pandemic: a systematic review.European journal of epidemiology · 2023Pooled it
- Clinical expressions, characteristics and treatments of confirmed COVID-19 in nursing home residents: a systematic review.BMC geriatrics · 2023Pooled it
- Inferring the true number of SARS-CoV-2 infections in Japan.Journal of infection and chemotherapy : official journal of the Japan Society of Chemotherapy · 2022Pooled 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
- BCG vaccination of healthcare workers for protection against COVID-19: 12-month outcomes from an international randomised controlled trial.The Journal of infection · 2024Trial
- Cost and cost-effectiveness of four different SARS-CoV-2 active surveillance strategies: evidence from a randomised control trial in Germany.The European journal of health economics : HEPAC : health economics in prevention and care · 2023Trial
- Comparison of Four Active SARS-CoV-2 Surveillance Strategies in Representative Population Sample Points: Two-Factor Factorial Randomized Controlled Trial.JMIR public health and surveillance · 2023Trial
- Impact of previous exposure to SARS-CoV-2 and of S-Trimer (SCB-2019) COVID-19 vaccination on the risk of reinfection: a randomised, double-blinded, placebo-controlled, phase 2 and 3 trial.The Lancet. Infectious diseases · 2022Trial
- Economic evaluation of wastewater surveillance in Ontario, Canada, using COVID-19 as a case study.Canada communicable disease report = Releve des maladies transmissibles au Canada · 2026Article
- Counterfactual evaluation of elementary and secondary school policies in the COVID-19 pandemic.Nature communications · 2026Article
- An integrative approach for studying immunological variation in an aging population - The Milieu Intérieur follow-up study.Nature communications · 2026Article
- Symptom Trajectories and Long-Term Sequelae of COVID-19: A Matched Case-Control Study with Population-Based Controls.Journal of clinical medicine · 2026Article
- Article
- Containment of a Multi-index B.1.1.7 Outbreak on a University Campus Through a Genomically Informed Public Health Response.Open forum infectious diseases · 2026Article
- Estimating the incidence of SARS-CoV-2 infections by jointly modelling seroprevalence, hospitalization and mortality data, February 2020 - January 2021, Belgium.Archives of public health = Archives belges de sante publique · 2026Article
- A Unique Patient Stratification Method Combined with a Machine Learning Approach Identifies Novel Genetic Susceptibility and Protective Factors for Severe COVID-19 in a Hungarian Population.International journal of molecular sciences · 2026Article
- Association between serum vitamins and COVID-19 infection: a cross-sectional study of healthcare workers in a Nigerian tertiary hospital.BMC infectious diseases · 2026Article
- Genetic, Sociodemographic and Clinical Determinants of COVID-19 Severity in the Republic of Srpska: Exploring Potential Links with Neanderthal-Derived Variants.Biomedicines · 2026Article
212 more citing papers are in PubMed but not listed here.
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Authors and funding
8 authors.
Funding
Abstract
Quantification of asymptomatic infections is fundamental for effective public health responses to the COVID-19 pandemic. Discrepancies regarding the extent of asymptomaticity have arisen from inconsistent terminology as well as conflation of index and secondary cases which biases toward lower asymptomaticity. We searched PubMed, Embase, Web of Science, and World Health Organization Global Research Database on COVID-19 between January 1, 2020 and April 2, 2021 to identify studies that reported silent infections at the time of testing, whether presymptomatic or asymptomatic. Index cases were removed to minimize representational bias that would result in overestimation of symptomaticity. By analyzing over 350 studies, we estimate that the percentage of infections that never developed clinical symptoms, and thus were truly asymptomatic, was 35.1% (95% CI: 30.7 to 39.9%). At the time of testing, 42.8% (95% prediction interval: 5.2 to 91.1%) of cases exhibited no symptoms, a group comprising both asymptomatic and presymptomatic infections. Asymptomaticity was significantly lower among the elderly, at 19.7% (95% CI: 12.7 to 29.4%) compared with children at 46.7% (95% CI: 32.0 to 62.0%). We also found that cases with comorbidities had significantly lower asymptomaticity compared to cases with no underlying medical conditions. Without proactive policies to detect asymptomatic infections, such as rapid contact tracing, prolonged efforts for pandemic control may be needed even in the presence of vaccination.
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Registered trials
Read under generation 80e0d062 · epoch 390. Bibliography from PubMed, PubMed Central and OpenAlex; grants from NIH RePORTER; trial links from ClinicalTrials.gov; estimates, votes and beliefs from the OpenQuestion graph.