WASHINGTON (AP) — The Defense Department has begun barring the enlistment of would-be military recruits who have been hospitalized for the coronavirus, unless they get a special medical waiver.

Under a Pentagon memo signed Wednesday, applicants who have tested positive for the virus but did not require hospitalization will be allowed to enlist, as long as all health and other requirements are met.

Those recruits who tested positive won't be allowed to begin the enlistment process until 28 days after the diagnosis, and they'll be required to submit all medical documentation. They'll be cleared for military service 28 days after they're finished with home isolation, and they won't need a waiver.

The Associated Press obtained a copy of the guidelines, which say that people who were hospitalized may have longer-term physical limitations. Those people would be considered "permanently disqualified" but could then be allowed to request a waiver from the military service they want to enter.

The military services could then require additional medical testing or evaluation as part of that waiver process to determine if the applicant should get a waiver and be allowed to enlist. The new requirement adds COVID hospitalization to a long list of medical conditions — such as asthma — that require waivers.

It is unclear how many potential recruits could be affected by the new guidelines.

Some patients hospitalized with the virus have suffered lung damage. Long-term lung damage could hinder recruits from passing grueling physical requirements for military services.

"Residual and long-term health effects for individuals with severe outcomes, such as hospitalization or admission to an intensive care unit from COVID-19 are unknown," the memo said.

For most people, the new coronavirus causes mild or moderate symptoms, such as fever and cough that clear up in two to three weeks. For some, especially older adults and people with existing health problems, it can cause more severe illness, including pneumonia, or death.