Asymptomatic SARS-CoV-2 infections tend to occur less frequently in developed nations

Unlike severe infections, asymptomatic infections occur independently of healthcare access and reflect the natural immunity to SARS-CoV-2. What determines their prevalence, ψ , and its variation across nations is unknown. We conducted a systematic review of serosurveys performed on samples representative of national populations before vaccination and the emergence of variants. The studies that met our selection criteria together sampled 4,58,489 individuals and yielded estimates of ψ in 33 nations. Using random-effects modeling, we found the pooled global ψ to be 45.3% (95% CI: 33.6%-57.5%). ψ varied widely across nations (range: 6%-96%; I 2=99.7%), highlighting the enormous underlying variation in the natural immunity to SARS-CoV-2. Performing meta-regression with national-level metrics, we found that the human development index (HDI) was negatively correlated with ψ (p=10−13; R 2=65.5%). More developed nations thus experienced less frequent asymptomatic infections on average. These findings have implications for unraveling the origins of asymptomatic infections and for future pandemic preparedness. ### Competing Interest Statement The authors have declared no competing interest. ### Funding Statement BC was supported by the C. V. Raman postdoctoral fellowship of the Indian Institute of Science. ### Author Declarations I confirm all relevant ethical guidelines have been followed, and any necessary IRB and/or ethics committee approvals have been obtained. Yes The details of the IRB/oversight body that provided approval or exemption for the research described are given below: N/A I confirm that all necessary patient/participant consent has been obtained and the appropriate institutional forms have been archived, and that any patient/participant/sample identifiers included were not known to anyone (e.g., hospital staff, patients or participants themselves) outside the research group so cannot be used to identify individuals. Yes I understand that all clinical trials and any other prospective interventional studies must be registered with an ICMJE-approved registry, such as ClinicalTrials.gov. I confirm that any such study reported in the manuscript has been registered and the trial registration ID is provided (note: if posting a prospective study registered retrospectively, please provide a statement in the trial ID field explaining why the study was not registered in advance). Yes I have followed all appropriate research reporting guidelines, such as any relevant EQUATOR Network research reporting checklist(s) and other pertinent material, if applicable. Yes All data produced in the present work are contained in the manuscript.