In updated guidance, the Centers for Disease Control and Prevention said its "best estimate" is that 40 percent of people infected with COVID-19 are asymptomatic.
In the update, posted July 10, the CDC said the basic reproduction number or the number of people one person "is likely to infect" is 2.5, and the infectiousness level of asymptomatic people is 75 percent, relative to symptomatic patients.
The government agency added a new part to its report, an "Infection Fatality Ratio," which "takes into account both symptomatic and asymptomatic cases and may therefore be a more directly measurable parameter for disease severity for COVID-19." The new metric states that 0.65 percent of those with COVID-19 are estimated to die.
Asymptomatic COVID-19 patients are of great concern to public health officials and lawmakers due to their ability to spread the virus without knowing they're sick themselves.
In June, an official from the World Health Organization said that spread from asymptomatic patients appeared to be "very rare." The comments were walked back a few days later following criticism from many in the scientific community, including Dr. Anthony Fauci, who said the statement was "not correct."
Separately that month, a study published by researchers in China found that asymptomatic patients had a weaker immune response to the virus.
As of Monday morning, more than 12.9 million coronavirus cases have been diagnosed worldwide, more than 3.3 million of which are in the U.S., the most impacted country on the planet.