2020 was a busy year for infectious disease physicians.

And as 2021 begins with hospitals already packed with COVID-19 patients, several doctors from Massachusetts hospitals say they worry infections from holiday gatherings will crowd ICUs even more.

"We're all sort of bracing ourselves," said Dr. Erica Shenoy, associate chief of the infection Control Unit at Massachusetts General Hospital. "What is it going to look like two weeks from now?"

Doctors say they expect a surge of hospitalizations to follow a spike in new infections by about two weeks.

"We are expecting to have a bump," said Dr. Cassandra Pierre, acting hospital epidemiologist at Boston Medical Center. "I don't know if it will be as dramatic as it was after Thanksgiving. Our airport travel tells us that it could certainly be as bad."

Right now, Pierre said, BMC projects it will have the capacity to meet the added demand. "I'm hoping that that continues to hold true, and that we are not surprised this time," she said.

Boston Medical Center, MGH and other hospitals around Massachusetts still aren't seeing anywhere close to the number of COVID-19 patients they cared for during the initial surge in the spring. At MGH, Shenoy said, they had about 125 COVID-19 patients on New Year's Eve, compared to about 400 during the peak in the spring.

But as the new year begins, the state is setting records for newly reported infections. The Department of Public Health reported nearly 6,900 confirmed cases of the virus as of Thursday, beating the previous all-time high set in early December. The DPH reports 190 communities, including Boston, are in the state's high risk "red zone." And if those numbers continue to climb, a surge of hospitalizations could follow.

"We could be seeing in a few weeks a very significant shortage of resources to take care of not just patients with COVID," said Dr. Shira Doron, hospital epidemiogist at Tufts Medical Center. "We can't forget that this is not about caring for COVID. This is about caring for absolutely anybody who needs medical care of any kind."

And an influx of patients could hamper the ability of hospitals to provide important care to other patients. At Tufts Medical Center, other medical units have already been converted into areas for adult COVID-19 patients.

"We are not business as usual right now in terms of our patient care operations," Doron said. "We have already expanded into nontraditional areas."

In early December, hospitals were ordered by Gov. Charlie Baker to scale back elective procedures, but they're still providing more care than they were able to during the initial surge.

In the spring, Shenoy said, many patients delayed necessary care.

"And as as much as we obviously are doing everything we can to to manage the COVID volume, the other part is to manage everything else ... and ensure that there's not harm that results from people staying away, and to make sure that we care for those who come to our door," Shenoy said. "I mean, that's the mission here."

Hospital capacity is particularly tight right now in the northeastern part of the state, where the Massachusetts DPH reported Thursday there were just 9% of ICU beds currently available and only 8% of non-ICU beds free.

"We are concerned about the impact of the holidays — both Christmas and now New Years — in contributing to a surge upon the existing surge," said Dr. David Longworth, president of Lahey Hospital and Medical Center in Burlington.

Longworth said he believes the lack of available hospital beds in the northeastern part of the state is the result of greater community spread of the virus in that region.

As 2020 drew to a close, infectious disease physicians looked back with a mixture of awe and disbelief.

It was a "momentous year," Longworth said. He's been an infectious disease physician since the AIDS epidemic of the 1980s.

"So I've spent a lot of time in health care," he said. "And this is the most consequential year in health care, in my opinion, in the last century. What we have lived through has been truly remarkable."

Longworth remarked on the scientific community's ability in just one year to identify the virus, genetically sequence it, and develop tests and effective therapies for it, as well as the creation of vaccines.

"That's a remarkable story, and it's a story that would not have happened five years ago or 10 years ago," he said.

The past year was also an exhausting year for those in healthcare.

"It's been incredibly intense, and I think everyone's very tired," Shenoy said. "But I think we have a lot to be proud of for the last year — and a lot of lessons learned that we're even applying now to the second surge, to do things better. I am really, really hopeful for 2021 and really grateful for all the hard work that people have put in across all different sectors."

For Pierre, the new vaccines bring a feeling of optimism.

"It is the first bright spot that we have had on the horizon for quite some time," she said. That's been tempered a bit, though, she said, "given that the rollout has been slower than we have expected nationally, and also in Massachusetts."

And, she pointed out, it will take as much as 72% of the population to be vaccinated before we can reach herd immunity.

"I think that there will be some time before we are able to achieve those numbers, unfortunately," she said.