Asymptomatic transmission is the basis of masks, distancing and general hysteria. For this reason it is important to understand the fallacy of this paranoia and senseless fear.
The below studies find the instance to be close to zero. Transmission of corona viruses and other influenza illnesses occur primarily only when symptoms are present and not from healthy asymptomatic people.

Covid-19: Asymptomatic cases may not be infectious, Wuhan study
indicates. Shaun Griffin bmj.com

Post-lockdown SARS-CoV-2 nucleic acid screening
in nearly ten million residents of Wuhan, China

The original study that postulated asymptomatic transmission on March 5th, 2020, involving a Chinese woman visiting Germany for business. She was in fact taking cold medication and symptomatic at the time. Christian Drosten, M.D., coauthor and a influential virologist in Germany, helped promote asymptomatic transmission as a reason for harsh public health restrictions.