Tom Inglesby, the director of the Johns Hopkins Center for Health Security, said on Sunday that the social-distancing measures taken in much of the U.S. to stem the spread of the novel coronavirus haven't yet had time to fully take effect.

"We're still at the very beginning of this outbreak," Inglesby told Chris Wallace Christopher (Chris) WallaceDemocrats urge Biden to resist filibuster, court-packing calls The Hill's Campaign Report: GOP set to ask SCOTUS to limit mail-in voting First presidential debate to cover coronavirus, Supreme Court MORE on "Fox News Sunday." "We should expect it to continue for some time and focus on social distancing as one of the main interventions to stop it."

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Wallace asked Inglesby about the possibility of certain regions of the country with low case numbers reopening businesses and allowing public gatherings while maintaining restrictions longer in harder-hit areas.

Inglesby said such steps could be a possibility in the future, but not while numbers are still rising in just about every state across the country.

He added, "I don't really have confidence that we really know where all the cases are," and said more widespread testing and improved treatment ability is a prerequisite for lifting social distancing measures.

The U.S. last week became the country with the most coronavirus cases in the world. As of Sunday morning, it had recorded more than 124,000 cases, according to Johns Hopkins University.

Inglesby said the U.S. should look to other countries where aggressive measures have been successful in curbing the spread of COVID-19.

When will the U.S. be back to normal? Doctor Inglesby weighs in: “Dates are hard to predict” but the Doctor thinks this should be a conditions based decision. #FNS pic.twitter.com/EuD4FWSLYt — FoxNewsSunday (@FoxNewsSunday) March 29, 2020

"What I think we need to do is really stick with what other countries who have had more success have done," Inglesby said. "They've largely been in Asia, Singapore, Hong Kong, South Korea, China, Taiwan, and they have put in place social-distancing measures until they've gotten control of the epidemic convincingly and at that point begun to try experimenting with loosening it. And I do think we will get to that point."

"But if we go back to work too quickly, this epidemic is going to spread widely and aggressively," he added.