Concerned citizens from Seoul to Paris, and Moscow to Bangkok,  are lining up for shots as COVID-19 case numbers spike. That may ease pressure on stretched hospitals around the world, but with it comes a hangover – a severe shortage of blood donors.

A number of countries don’t allow people who have just been inoculated to give blood, as well as banning those in recovery from coronavirus. With others simply staying home as new infections rise, doctors say donor pools have shrunk to alarmingly low levels, menacing urgent operations.

In South Korea, now wrestling with record cases, donors can’t give blood for seven days after a COVID-19 shot – and supply is down to just 3.2 days, as of Wednesday, from 6.5 days’ worth this time last year, according to the Korean Red Cross.

The Korean Medical Association (KMA) has launched a blood drive, starting with doctors themselves, warning that patients in need of urgent surgery or transfusions could face emergency situations, KMA spokeswoman Park Soo-hyun told Reuters.