In an interview with NBC News, Azar encouraged all Americans to follow the government's guidelines about social distancing and mask wearing.
Azar said that in many southern states where the virus is spiking -- including Florida and Texas -- the majority of the cases are people under 35, and a large number of those will be asymptomatic.
"We've got our fatality rates and our hospitalization rates are the lowest they've been in two months, but this is a very serious situation," he said.
Azar said the administration is working with local authorities and states to understand why the virus is surging in certain areas.
He noted that treatments like steroids and remdesivir are now available for COVID-19, and encouraged people who have had the virus to donate plasma to increase the supply.
More than 2,531,000 COVID-19 cases have been reported in the United States with the fatalities surpassing 125,600 as of Sunday afternoon, according to a tally by Johns Hopkins University.