Adm. Brett Giroir, assistant secretary for health in the Department of Health and Human Services, adjusts his face mask while testifying this month before a House subcommittee on the coronavirus crisis.

A recent analysis for NPR by Harvard researchers found that more than 1 million tests were needed to mitigate, or keep outbreaks from getting worse. Giroir said the U.S. is well on its way to this target.

He emphasized the need for public health measures in addition to testing, including social distancing and the wearing of masks. “We need places that are in hot zones to close bars and to limit restaurants. And if we do those simple things, we can turn around the virus,” he said.

Since then, testing for the coronavirus has become more widespread. But there continue to be shortages in the supplies and machines needed to get results.

Giroir acknowledged the growing wait times due to the “unprecedented demand.”

Delays in testing mean public health workers are not able to notify the contacts of people who test positive, and so people may unwittingly continue to spread the virus.