This meta-analysis sought to estimate the pooled prevalence of asymptomatic monkeypox virus (MPXV) detections in nonendemic regions during the period May 12, 2022–September 13, 2024. The investigators used PubMed as the primary search database with the following search logic combining asymptomatic-related terms (e.g., asymptomatic, no lesion*, undetected) and MPXV-related terms (e.g., monkeypox, mpox, MPXV). Additional relevant articles were obtained from citations within screened studies. The authors limited inclusion to articles published in the specified date range to capture evidence relevant to the ongoing outbreak that began in 2022.
Study selection followed the Preferred Reporting Standard of Systematic Reviews and Meta-Analysis (PRISMA) approach. The initial screening removed titles that clearly did not address asymptomatic MPXV detections; abstracts of excluded articles were briefly reviewed. Full-text review of candidate articles was performed independently by two co-authors, with a third consulted to resolve disagreements. The authors did not prospectively register a review protocol.
Inclusion criteria required studies to meet all of the following: be primary research conducted outside sub-Saharan Africa (nonendemic regions), include adult participants (>18 years), report individual-level counts (not ecological summaries), and perform PCR testing for MPXV. PCR testing in included studies used sample types such as pharyngeal, anorectal, urethral swabs, urine, or blood. Crucially, studies had to explicitly state that persons were asymptomatic—described as asymptomatic, undetected, clinically inapparent, or explicitly without lesions or rashes. Any mention of symptoms excluded a person from the asymptomatic category, and articles that did not otherwise provide clear asymptomatic data were excluded. The authors initially considered vaccination status but did not include it as an inclusion criterion because few studies reported vaccination.
For each included study, the team extracted author(s), study design (cross-sectional, prospective cohort, retrospective cohort, mixed), publication date, recruitment dates, country, counts of asymptomatic MPXV detections, and total number tested. The JBI critical appraisal checklist for prevalence studies was applied to determine study eligibility.
For analysis, prevalence of asymptomatic MPXV detections was calculated as the number of asymptomatic PCR-positive detections divided by the total number of people tested in each study. The authors constructed a funnel plot and statistically assessed bias among included studies. They used random-effects logistic regression models to estimate pooled prevalence and corresponding 95% prediction intervals (PIs), which account for between-study heterogeneity.
The meta-analysis pooled results from studies published during the defined search window; the random-effects analysis produced a final pooled prevalence estimate of 1.0% for asymptomatic MPXV detections. The 95% prediction interval around this estimate was 0.1%–11.2%. The authors report that results did not substantially differ when stratified by geographic region or by study design, indicating relative consistency across the included nonendemic settings and study types.
The manuscript contrasts these findings with an earlier systematic review and meta-analysis that estimated a pooled prevalence of 10.2% (95% CI 2.5%–17.9%) but included reports up to September 2022 and studies not specific to the 2022 global outbreak (including an outbreak in a primate sanctuary). The present review restricted study settings to nonendemic regions and to the period corresponding to the ongoing outbreak, which the authors argue improves relevance to current transmission dynamics primarily affecting certain human populations.
The authors also summarize individual study findings that illustrate variability in reported asymptomatic detection. Several reports noted absence of asymptomatic detections in their study populations, while retrospective screening studies in France and Belgium that analyzed anorectal, urine, and oropharyngeal samples found higher prevalences (reported in source studies as 5.5% and 1.3%). The authors emphasize a key methodological limitation: detection of viral genetic material by PCR does not equate to confirmed infectiousness.
The meta-analysis concludes that the pooled prevalence of PCR-detected asymptomatic MPXV in nonendemic regions during May 2022–September 2024 was about 1.0% (95% PI 0.1%–11.2%). The authors note that these results are reassuring in suggesting a relatively low pooled prevalence across included studies, and they report no substantial differences by region or study design in the pooled estimates.
However, important limitations are highlighted. First, PCR detection of viral genetic material does not necessarily indicate that an individual is infectious; the study did not assess infectivity or transmission potential of persons who remained asymptomatic. Second, the review used PubMed as the single primary database due to resource constraints and did not prospectively register the review protocol. Third, few included studies reported vaccination status, so the potential modifying effect of prior vaccination on asymptomatic detection could not be evaluated.
The authors contextualize their findings by noting that most transmissions in the United States during the outbreak have been person-to-person, primarily through sexual contact among gay, bisexual, and other men who have sex with men (GBMSM), and that MPXV can be transmitted in the 1–4 days before symptom onset. Yet whether truly asymptomatic infections contribute meaningfully to transmission remains unclear and was not addressed by the pooled prevalence analysis.
In closing, the authors state that MPXV continues to circulate globally and that the viral dynamics that enable its persistence are poorly understood. They call for further study to clarify the role, if any, of asymptomatic infections in transmission and in sustaining viral circulation.