CVS Health Chief Executive Larry Merlo said a lack of personal protective equipment has slowed the widespread rollout of its drive-thru tests for the coronavirus and limited the number of tests that sites are able to do.

In an interview on "Closing Bell," he said CVS is working closely with Walmart, Walgreens and Target to make tests more readily available.

"One of the rate-limiting steps is the availability of protective gear for those that are manning those sites, and that's something that we're working through," Merlo said.

Workers at the drive-thru tests must wear gowns, masks and gloves as they swab a patient for a sample. They must change that gear after each person to avoid getting the next person sick.

Leaders of the four retailers, including CVS, met with President Donald Trump at the White House on March 13 and committed to having drive-thru testing sites in their parking lots. So far, CVS has one test site, Walmart has two and Walgreens has one. Target has not yet announced when test sites may open near its stores.

Thus far, all of the test sites are limited to first responders and health care workers.

Last week, Walmart's Executive Vice President of Corporate Affairs Dan Bartlett attributed the delay to supply issues, too. He said it has had trouble getting test kits and finding masks, gloves and other personal protective gear for workers.

CVS opened its first test site last week in Massachusetts. The site is in Shrewsbury, a suburb in Worcester County. It's taken a hands-on role with its test site: It staffed the facility near its store with its own employees, such as nurse practioners. Walmart's and Walgreens' sites are staffed by government workers.

Merlo said the company has learned a lot from the first site, but he did not say when or where it may open additional ones.

He said the site can do 100 to 110 tests per day and has seen high demand. "The tests are actually booked almost through the end of this week," he said.

One of the lessons, he said, is how the company could scale up to more drive-thru lanes. In Massachusetts, he said CVS can only fit one drive-thru lane, but he would like to take its concept to larger nearby parking lots, such as at schools and open two, three or four drive-thru lanes to "get as many as 500 tests done a day."

Along with testing, CVS is in the middle of an aggressive effort to fill 50,000 jobs, from store associates to home delivery drivers, as it deals with a growing demand for over-the-counter medicines, prescriptions and other health-care services.

It is also giving bonuses, ranging from $150 to $500, to pharmacists, store associates and other employees who must be on-site at CVS facilities, to recognize their work during the pandemic.