Europe’s Covid-19 crisis is moving eastward, from the wealthiest and best-prepared countries on the continent into the poorer states that have exported doctors for decades. Now, as Covid-19 cases soar, the bill from that long exodus is coming due.

With 238 physicians per 100,000 people, Poland has the lowest such ratio in the European Union, nearly half the level of Germany, whose relative success in handling the virus owes much to its foreign staff. The average age of Polish nurses is 53, just seven years short of retirement.

Largely spared during the spring surge, Hungary, Slovakia, Poland and Romania braced for autumn by stocking up on ventilators. But they lack people to operate the equipment. As cases pile up, shifts that often spanned two full days before the pandemic are now stretching the limits of human endurance.

“It’s hard times, I think, it’s like the Second World War,” said Dr. Rotnicki, who arrived on a recent Friday morning at the Independent State Healthcare Hospital in Międzychód in western Poland and didn’t clock out until the following Monday. Hours later, three of his patients died. “I had to go home because I thought, I will maybe kill somebody,” he said.