Occurrence and transmission potential of asymptomatic and presymptomatic SARS-CoV-2 infections: Update of a living systematic review and meta-analysis
PLOS Medicine·
- DOI
- 10.1371/journal.pmed.1003987
- PMID
- 35617363
- PMCID
- PMC9135333
- OpenAlex
- W4281550495
- Study type
- Systematic review
- Publisher
- Public Library of Science (PLoS)
- Article type
- journal-article
- Integrity
- current
Publication version
This article has a linked preprint
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Open linked preprint →Why this research matters now
The review supports a characterisation in which most SARS-CoV-2 infections are not persistently asymptomatic and asymptomatic infections are less infectious than symptomatic ones, while highlighting that extreme between-study variability limits any single pooled estimate.
Structured evidence summary
Research question
The review addresses three questions: the proportion of SARS-CoV-2 infections that remain asymptomatic throughout follow-up, the infectiousness of asymptomatic and presymptomatic infections relative to symptomatic ones, and the population-level share of transmission attributable to asymptomatic or presymptomatic individuals.
Study design
An updated living systematic review and meta-analysis pooling empirical and mathematical modelling studies, with single-reviewer extraction verified by a second reviewer and risk-of-bias assessment using bespoke and published checklists.
Population and setting
Populations with PCR-diagnosed SARS-CoV-2 infection drawn from screening of defined populations, contact or outbreak investigations, and mathematical modelling studies, searched in PubMed, Embase, bioRxiv, and medRxiv up to 6 July 2021.
Main findings
Across 130 studies, heterogeneity was too high for an overall pooled asymptomatic proportion (IQR 14%–50%; prediction interval 2%–90%); 46 contact/outbreak studies yielded a summary estimate of 19% (95% CI 15%–25%). The secondary attack rate ratio for contacts of asymptomatic versus symptomatic index cases was 0.32 (95% CI 0.16–0.64) across 8 studies. In 13 modelling studies, presymptomatic individuals accounted for more modelled transmission than asymptomatic individuals.
Public-health relevance
The review supports a characterisation in which most SARS-CoV-2 infections are not persistently asymptomatic and asymptomatic infections are less infectious than symptomatic ones, while highlighting that extreme between-study variability limits any single pooled estimate.
Important limitations
Stated limitations include high heterogeneity, high risk of selection and information bias in studies not designed to measure persistent asymptomatic infection, and limited information on variants of concern and vaccinated populations. The protocol-based design excludes single-individual or family studies and studies without sufficient follow-up, which may further narrow generalisability.
GIDS interpretation
Indexed under SARS/COVID-19 with links to outbreak investigation, transmission dynamics, and vaccination topics, suggesting placement within respiratory-virus transmission and surveillance literatures; this summary does not connect the review to any live surveillance signal.
Related GIDS surveillance
Literature context does not validate, explain, or change a surveillance signal. Exact and contextual relationships are shown separately.
Evidence relationships
This article has 10 auditable classifier relationships to diseases, places, topics, and study design.