Most transmission of the coronavirus is coming from people who are asymptomatic and never develop any symptoms, a top official from the Department of Health and Human Services said Friday. 

“Just feeling like you want to go get a test is really not the best strategy, but we know that most of the spread are from asymptomatic people, particularly young adults, so you have to cast a wide net and I think we’re able to do that,” Adm. Brett Giroir, the assistant secretary for HHS, said in an interview on CNBC’s “Squawk Box.”

An asymptomatic person is someone with Covid-19 who doesn’t have symptoms and never develops them. Scientists have found that people who don’t have symptoms can spread the virus. That includes asymptomatic people as well as people in the pre-symptomatic stage a few days before they start to show signs of the virus.

The comment by Giroir comes as the virus continues to rapidly spread across the United States. The U.S. reported 77,255 new cases of the coronavirus on Thursday, shattering its previous record single-day spike in new cases by nearly 10,000, according to data compiled by Johns Hopkins University.

State and federal health officials say more young people, who may otherwise appear healthy, are ignoring social distancing measures and contracting the virus at a higher rate. However, they say even people who never develop symptoms can also pass the virus on to others.

Dr. Anthony Fauci, the nation’s leading infectious disease expert, said Thursday that asymptomatic people carry as much virus as people who are symptomatic.

“When you measure the level of virus in the nasal pharynx of asymptomatic people, compared to people who are symptomatic, there doesn’t seem to be any difference, which means there’s as much virus in the nose of a person who’s asymptomatic as there is in a symptomatic person,” Fauci, director of the National Institute of Allergy and Infectious Diseases, told Facebook CEO Mark Zuckerberg in an interview. 

Giroir said Friday that Covid-19 is “not the flu,” adding the U.S. needs to allow asymptomatic people to be tested.

“When I talk about unnecessary testing, we know that there’s a lot of people who are being asked to retest themselves at the end of their illness and some people are getting test four, five, six times and that’s just really unnecessary,” he said.

“According to the guidelines, if you’re ten days since the onset of your illness and at least three days asymptomatic, you’re fine,” he said. “It’s like whoever has the flu, you never go back and get test two or three times for the flu.”

This is a developing story. Please check back for updates.