Ms. Stevenson, an intensive care unit nurse at Eskenazi Health in Indianapolis for the past seven years, cries as she talks about her patients and their families, making clear the grinding toll of the pandemic on already exhausted hospital work forces.

“We’re pretty short-staffed,” Ms. Stevenson said. She added: “It’s getting harder.”

Instead of taking holiday vacations this weekend, workers at strained hospitals across the nation are working 16-hour shifts. Some have been on the job every day for weeks. Festive meals have been replaced with protein bars and sports drinks.

This Christmas weekend, with the United States facing another surge of illness stoked by a proportion of the population that remains unvaccinated, frontline workers are again sacrificing time at home with family to tend to Covid patients. In Indiana, which has among the highest rates of hospitalization and lowest rates of vaccination in the country, the situation is especially acute.

“A lot of people, including myself, had scheduled time off but are now being asked to come in and pick up shifts to cover for one another and meet the increased demands of patient care,” said Dr. Graham Carlos, the executive medical director at Eskenazi, which is at capacity and has had a backlog of patients in the emergency room.

He worries that it will only get worse. “If the numbers continue as they are, a tidal wave of infections is going to hit hospital systems, putting us in dire straits,” he said.

Nearly two years into the pandemic, hospital workers have already faced the emotional toll of mass death. They have endured the frustration of pleading with the public to take precautions, only to watch outbreaks unfold as people ignored their calls. They have suffered the moral distress of not being able to give patients the ideal level of care.

But this season, there is a new strain: Many workers have left because of burnout and anxiety. And with the Omicron variant pushing case numbers up dramatically, the caregivers who remain are getting infections, too.

“This is the worst I’ve ever seen it,” said Maureen May, a nurse with 37 years of experience who serves as president of the Pennsylvania Association of Staff Nurses and Allied Professionals. She canceled her own holiday plans to pick up a shift on Christmas Day so that a co-worker could have time away.

Facing urgent concerns about hospital staffing shortages, the Centers for Disease Control and Prevention this week shortened the isolation periods for infected health care workers, allowing them to return to the job in seven days, instead of 10. President Biden also said that 1,000 military doctors, nurses, paramedics and other medical personnel would be deployed to shore up staffing levels at hospitals in the coming weeks.

At IU Health Methodist Hospital in Indianapolis, the National Guard has been helping with tasks such as transporting patients and cleaning. Now, a 20-person Navy team is arriving to help supplement the medical staff, which is depleted in part because about 350 workers across the broader hospital system are out with Covid or because they have been exposed to the virus.