Thirty prisoners have active COVID-19 cases, most of them housed at the Souza-Baranowski Correctional Center in Lancaster, state officials said Tuesday.

The data released by the Massachusetts Department of Correction marks a jump in the number of COVID-19 cases in the state’s incarcerated population. Last month, zero COVID cases were reported among prisons who published data.

The resurgence of the disease in the state’s prison system comes as the highly contagious delta variant raises growing concerns across the country. Elizabeth Matos, executive director of the Boston-based Prisoners’ Legal Services, said the state needs to do more to protect prisoners from the deadly virus, including increasing vaccinations among correctional staff.

About 57% of DOC staff and 78% of prisoners are fully vaccinated, state officials say.

Matos says she’d like to see the state require vaccinations among prison staff the same way officials are requiring vaccinations in nursing homes. Last week, state officials announced plans to require most nursing home workers to be fully vaccinated by Oct. 10

“We’re seeing the governor enforce a vaccine mandate for folks who work in some congregate settings, but no mention of jails and prisons,” Matos said. “We're continuing down this path of not treating this population seriously.”

DOC officials said the state is doing its best to keep prisoners safe, including launching an education campaign to encourage vaccinations and requiring face coverings to all those entering its facilities.

“Every decision aligns with the latest state and federal public health guidance and focuses on mitigating the virus’ ability to enter and transmit within facilities,’’ said DOC spokeswoman Cara Savelli. “The department takes immediate action to respond to any new cases and minimize transmission.”