COVID is raging at some, but not all, congregate care facilities in Mass.

With coronavirus cases spiking in Massachusetts, rates of infection were mixed in some places where the virus would be expected to spread the fastest: congregate care facilities, where groups of people live together in close quarters.

State data suggest that so far in some congregate care facilities, there has been no spike in cases. In others, the jump is dramatic.

The biggest spike in positive coronavirus tests was observed inside group homes for people with intellectual and developmental disabilities that are run operated by private vendors, according to state data released on Dec. 28. The data show that on Dec. 1, there were 34 positive cases among residents of such homes. The latest tally showed cases climbed to 146 by the end of December.

"That's a signal that there's a problem," said Rick Glassman, director of advocacy for the Disability Law Center. "We need to do more to get infection under control."

More than 7,700 people live in group homes overseen by the state Department of Disability Services (DDS) and most are run by private vendors. Glassman said although workers at state-run group homes are required to be vaccinated, workers in privately run homes are not. Regardless of staffing shortages facing some homes, Glassman said vaccines should be mandated for all group home workers, and there should be more frequent testing of both residents and workers.

"It is to the state's credit that they require vaccines in nursing homes," Glassman said. "But people with intellectual and developmental disabilities are equally, and sometimes more, vulnerable."

State data on nursing home infection rates are difficult to decipher. Some say the numbers may not yet reflect an expected post-holiday spike.

Dr. Larissa Lucas, medical director of extended care for North Shore Physicians Group, said recently, there were more cases among residents in the seven nursing homes she works with, but nowhere near the spikes seen at earlier stages of the pandemic. She said no residents have gotten severely ill from the virus.

"We haven't had many hospitalizations or deaths due to COVID specifically," Lucas said, "and we've been able to administer monoclonal antibodies when appropriate. So I'm happy to say that, yes, our infections have been mild in our vaccinated residents."

Lucas said there were higher infection rates among nursing home workers, even though about 60% of staff at the seven nursing homes received vaccine booster shots. She said workers and residents are regularly tested, with most testing at least weekly. Visitors, she said, remain a big concern, as they cannot be required to be vaccinated before entering the homes.

"If someone is coming to visit a loved one in a nursing home, please make sure you're vaccinated," Lucas said. " Always wear a mask when you're in the building and take a test if you can; we have tests available. We have to protect our vulnerable."

The infection rate in Massachusetts Department of Public Health congregate care facilities doubled in December. Those facilities include residential addiction treatment programs licensed by the state. Infection rates also were up at facilities run by the Department of Mental Health, the Department of Youth Services and group homes run by the Department of Children and Families (DCF).

State prisons were another place where the virus easily spread in 2020, but the state Department of Correction said there are few infections now.

As of Monday, the DOC said there were a total of 11 positive cases in state prisons — five at Bridgewater State Hospital, three at the Massachusetts Alcohol and Substance Abuse Center at Plymouth, two at MCI Cedar-Junction and one at MCI-Framingham. The DOC said "testing and screening continue throughout the agency."