As many as 25 percent of people with the coronavirus may never show symptoms, says Centers for Disease Control and Prevention (CDC) Director Robert Redfield.

In a Monday interview with NPR, Redfield said that COVID-19, the disease caused by the new coronavirus, spreads “far easier” than the flu, in part because it appears people can spread the virus up to 48 hours before they feel sick, if they even show symptoms at all.

“This helps explain how rapidly this virus continues to spread across the country because we have asymptomatic transmitters and we have individuals who are transmitting 48 hours before they become symptomatic,” he said.

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The virus is spreading quickly in the U.S., with 165,870 cases confirmed as of Tuesday morning.

Because there is still not widespread testing for COVID-19 in the U.S., it’s not known how many people actually have it.

The federal government is urging people to practice social distancing measures, such as working from home and staying at least six feet away from others, to slow the spread of the virus and prevent an influx of patients from overwhelming the health care system.

It is especially important for people who appear healthy to follow those measures since they could carry the virus to more vulnerable populations.

“So this social distancing that we're pushing ... is a powerful weapon, and that will shut this outbreak down sooner than it otherwise would have been shut down,” Redfield said.

Redfield said he expects transmission of the disease to decrease in the U.S. in the late spring and early summer, but the CDC is preparing for a second wave to hit in the fall or early winter.

“Hopefully, we'll aggressively re-embrace some of the mitigation strategies that we have determined had impact, particularly social distancing,” he said.