WASHINGTON (AP) — The U.S. surgeon general on Thursday urged healthy Americans, especially younger ones, to donate blood as supplies dwindle amid the coronavirus outbreak.

“Social distancing does not have to mean social disengagement,” Dr. Jerome Adams said, noting that blood centers are taking extra precautions so people can safely donate.

Supplies already are tight in parts of the country. The bigger concern is that blood has a short shelf life and the regular donations needed to replenish expiring stocks are drying up. Retirees, among the most reliable blood donors, are heeding calls to stay home. With college campuses closed and corporate blood drives called off as employees work from home, younger people aren’t filling the void.

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“It’s lost in the shuffle of everything else now,” said Dr. Brian Williams, who co-directs the University of Chicago’s surgical intensive care unit. But “trauma and emergency surgeries are not decreasing as a result of the pandemic.”

The industry has counted more than 12,000 blood drives canceled, some immediately and others set for coming months. So far, 355,000 fewer blood donations are projected because of the coronavirus outbreak, AABB, formerly called the American Association of Blood Banks, said Thursday. Its website lists donation centers.

Red blood cells last for 42 days, platelets just five days, and some blood types are more rare than others. Already, blood centers have sent hospitals tips on how to stretch supplies.

The new coronavirus can’t be spread through blood, either getting or giving it. And the message for would-be donors: Answering a call for a local blood drive isn’t violating the message to avoid crowds.

“A blood center environment is going to be safer than another more public area like a grocery store,” said Dr. Suchi Pandey, chief medical officer of Stanford University’s blood center, which filled appointments Thursday for a mobile drive.

Just like before the outbreak, would-be donors must be healthy, with no fever or other signs of illness. Among extra precautions being taken now: Donors are spaced at least 6 feet apart in fixed blood centers; workers who draw blood have their temperatures regularly checked; and spaces get extra disinfection. When Stanford does a mobile drive, it’s allowing fewer donors on the bus at a time.