In a briefing with reporters Thursday, CDC Director Robert Redfield said surveys of blood samples taken from around the country suggest that millions of Americans may have contracted the virus either without knowing it or with only minimal symptoms.
For every one confirmed case, Redfield said, the CDC estimates that 10 more people have been infected.
This virus causes so much asymptomatic infection," Redfield said. "We probably recognized about 10 percent of the outbreak."
Almost 2.4 million Americans have tested positive for the coronavirus, according to the Center for Systems Science and Engineering at the Johns Hopkins University of Medicine. Redfield said the serological surveys of blood samples, collected both for coronavirus tests and for other reasons like blood donations or laboratory tests, showed that between 5 percent and 8 percent of Americans have contracted the virus.
Most people who contract the SARS-CoV-2 virus show few if any symptoms, and only a small percentage require hospitalization. But while the number of potentially infected people is multitudes higher than the number of confirmed cases, Redfield also said the relatively low percentage of Americans who have been infected means hundreds of millions more remain at risk.
"This outbreak is not over. This pandemic is not over. The most powerful tool that we have, powerful weapon, is social distancing," Redfield said. "We have responsibility to practice the social mitigation strategies to protect the vulnerable, to protect the elderly."
CDC officials are warily eyeing growing numbers of coronavirus cases and hospitalizations in Southern and Southwestern states, Redfield told reporters in a conference call. More than 100 CDC staffers are deployed to about 20 states to help local health departments deal with the exploding number of cases.
Case counts have grown especially in states like Arizona, Florida, Hawaii, Kansas, Nevada, Ohio, Oklahoma, South Carolina, Texas and West Virginia, all states where the average daily number of confirmed cases has doubled or more in the past two weeks. Hospitalizations are on the rise in many of those states, and Texas and Arizona officials have both sounded the alarm in recent days about dwindling hospital capacity.
On the other hand, there are signs of hope in some of the earliest epicenters of the outbreak. New York Gov. Andrew Cuomo (D) said Thursday that his state was treating fewer than 1,000 COVID-19 patients in hospitals, the first time since mid-March that the number of hospitalized cases had dipped below 1,000.
Hospitalizations are declining in Connecticut, Washington, D.C., Illinois, Indiana, Maryland, Massachusetts, New Hampshire, New Jersey, Pennsylvania and Rhode Island, as well.
"We're not talking about a second wave right now, we're still in the first wave. And that first wave is taking different shapes," Redfield said.