Staff and inmates inside county jails and state prisons are among the next group of people in line for COVID-19 vaccinations.

Massachusetts is one of just eight states making the vaccine available to prisoners during the first phase of vaccinations, according to the Prison Policy Initiative.

COVID-19 Vaccine Advisory Group Chairman, Dr. Paul Biddinger, said that decision was driven by data.

People living and working in places like nursing homes and prisons — where social distancing is difficult — often have pre-existing conditions that make them more susceptible to the virus, he said.

“If we had enough vaccine in Massachusetts, we would want everyone to be vaccinated today,” he said. “But [we are] trying to move through the Commonwealth in the way that saves the most lives, that promotes equity, that is effective in getting virus prevalence down in the communities.”

More than 260 doses have already been given to health care staff within corrections facilities, according to the state Department of Public Health.

Biddinger said the next phase of vaccinations will likely happen in January. But distribution is heavily dependent on vaccine production and supply.

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