May 31, 2022

Occurrence, transmission of asymptomatic vs symptomatic COVID-19 infections

By: Judy Mathias

Editor's Note

Based on this update of a systematic review and meta-analysis of 130 studies, led by researchers from the University of Bern, Switzerland, most COVID-19 infections were not persistently asymptomatic, and asymptomatic infections were less infectious than symptomatic infections.

Because of variability among studies, the meta-analysis did not calculate a single estimate of the rate of asymptomatic infections, but the inter-quartile range was estimated to be at 14% to 50%.

The secondary attack rate, which is a measure of the transmission risk of COVID-19, was approximately two-thirds lower for those without symptoms than for those with symptoms, a risk ratio of 0.32.

Future studies should determine the asymptomatic proportion of COVID-19 infections caused by variants and in people with immunity following vaccination or previous infection, the authors note.

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