About 40 percent of COVID-19 infections asymptomatic: U.S. CDC

Around 40 percent of positive COVID-19 cases showed no symptoms of the coronavirus disease, according to the latest "COVID-19 Pandemic Planning Scenarios" from the U.S. Centers for Disease Control and Prevention (CDC).

This document, which the agency said can be used to estimate the possible effects of COVID-19 in U.S. states and localities, was first posted on May 20. The July 10 update is based on data received by the U.S. CDC through June 29. 

Under the CDC's "current best estimate," 40 percent of people with Covid-19 are asymptomatic. This number is up from 35 percent the agency estimated on May 20. The percent of asymptomatic cases remains uncertain, the CDC emphasized.

Also, under the agency's current best estimate, an asymptomatic individual is 75 percent as infectious as an asymptomatic individual. 

"Asymptomatic cases are challenging to identify because individuals do not know they are infected unless they are tested, which is typically only done systematically as a part of a scientific study," the CDC said.