Gov. Janet Mills’ announcement Thursday that all health care workers must be fully vaccinated against COVID-19 by Oct. 1 puts health care facilities in the region where vaccinations rates are low on a tight deadline to boost numbers.

Workers at all state-licensed hospitals, residential care facilities, home health agencies, dental practices and emergency medical service organizations have until Sept. 17 to get their final shots so they are fully immunized by the Oct. 1 deadline.

Full immunization against COVID-19 occurs two weeks after the final dose is administered.

“It’s an aggressive but achievable time frame for anyone who has not been vaccinated yet to still get their first and second dose of COVID-19 vaccine, plus the two-week wait period,” Mills said at a media briefing Thursday.

Maine Center for Disease Control and Prevention Director Dr. Nirav Shah and Department of Health and Human Services Commissioner Dr. Jeanne Lambrew were also at the briefing.

That leaves area hospitals, which employ more health care workers than any of the other facilities in the region, with the most catching up to do, according to health care worker vaccination rates published by DHHS on Thursday. The state began requiring in May that health care facilities, including hospitals, residential care facilities and nursing homes, submit their monthly staff vaccination rates.

At Central Maine Medical Center in Lewiston, nearly 900 out of about 2,600 staff members have yet to be vaccinated, meaning 66% have been vaccinated as of July 31. According to the report, only three employees were vaccinated in the month of July.

“Our focus remains on education, providing a safe and caring workplace and making vaccination accessible and convenient for our team members and communities,” Dr. John Alexander, chief medical officer for Central Maine Healthcare, CMMC’s parent organization, said in a statement following the briefing.

“Because vaccination provides the best protection against COVID, these will continue to be our priorities as we evaluate the implications of the governor’s announcement and implement this policy throughout our health system,” he said.

Statewide, 80% of all hospital health care workers have been vaccinated, according to DHHS.

At Bridgton and Rumford hospitals, also part of CMH, about 85% and 75% of staff are fully vaccinated, respectively, though each hospital’s smaller staff size — both employ around 150 people — leave fewer people left to reach.

At Lewiston’s other hospital, St. Mary’s Regional Medical Center, about 260 people will need to get vaccinated within the next five weeks. Nearly 83% of staff are fully inoculated as of the end of last month, a 10% increase from the end of June.

“We’re happy about that but obviously, we strive to get even closer to 100%,” St. Mary’s Health System spokesperson Steve Costello said Thursday afternoon.

Costello said he “suspected” the mandate announced Thursday was coming, given Mills’ statement earlier this week that followed the news of outbreaks among staff at Portland’s Maine Medical Center and Belfast’s Waldo County General Hospital, but that St. Mary’s Health probably won’t have a plan in place to meet the deadline until early next week.

“There are still some questions that need to be answered,” such as what constitutes a medical exemption from the mandate, Costello said.

“I would think by early next week we’ll have a plan in place and obviously, we want to reach out to our employees and give them the information on what it is that we are looking to do.”

Stephens Memorial Hospital in Norway and Franklin Memorial Hospital in Farmington are part of MaineHealth. The state’s largest hospital system said last week that it would require COVID-19 vaccinations as a “condition of employment,” effective Oct. 1.

Staff at Stephens Memorial are 78% vaccinated and staff at Franklin Memorial are 71% vaccinated.

Of the 35 hospitals that reported their July numbers to the state, Franklin Memorial and CMMC had the third- and second-lowest vaccination rate, respectively. Sebasticook Valley Health in Pittsfield had the lowest vaccination rate but was only a tenth of a percentage point behind CMMC.