30 to 60 percent of the spread of Coronavirus worldwide is from people with no symptoms at all

It is now widely accepted that seemingly healthy people can spread the virus, though uncertainty remains over how much they have contributed to the pandemic. Though estimates vary, models using data from Hong Kong, Singapore and China suggest that 30 to 60 percent of spreading occurs when people have no symptoms.

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https://www.nytimes.com/2020/06/27/world/europe/coronavirus-spread-asymptomatic.html