Last updated by The POOG on July 14, 2020

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In the early stages of the disease, detection of infected individuals depended largely on their having symptoms serious enough to send them seeeking medical care at which point testing may be done. There were neither the resources nor the inclination to perform tests on the general population seeking asymptomatic infected individuals.

Over time, for proper epidemiological assessment, small studies were done on selected populations to assess the percentage of asymptomatic infections.

A Review of Some Studies

A Spanish study[1] of 35,883 households reported that:

Our findings confirm that at least a third of individuals who have developed antibodies against SARS-CoV-2 were asymptomatic.


Summary of Results


  1. Marina Pollán, Beatriz Pérez-Gómez, Roberto Pastor-Barriuso, a, et al. Prevalence of SARS-CoV-2 in Spain (ENE-COVID): a nationwide, population-based seroepidemiological study. Lancet. July 06, 2020. DOI: