AUGUSTA, Maine — All Mainers age 16 and older will be eligible to receive a COVID-19 vaccine starting Wednesday after Gov. Janet Mills moved universal eligibility up nearly two weeks from a previous plan.

The decision to make younger Mainers eligible for the vaccine sooner comes as the virus has shown little sign of slowing in Maine despite the accelerated vaccination rollout, and as appointments have been slower to fill as supply has grown. Vaccine sites can begin accepting appointments for younger Mainers now, Mills said, though most were not Thursday afternoon.

As of Thursday, Maine administered 435,700 first doses of the Pfizer and Moderna vaccines as well as more than 277,000 second doses and one-shot Johnson & Johnson vaccines. The state’s vaccine supply has picked up noticeably in recent weeks, with enough doses to cover 68,000 new patients this week. The state’s federal allocation is increasing again next week.

“While this is a great step forward, Maine people should keep in mind that even though they are eligible it will still take time to get an appointment and get a vaccine,” Mills said.

State officials touted the vaccine Thursday as an important tool for Maine to combat the spread of coronavirus variants, which are likely a factor contributing to Maine’s continued spread of the virus even as 20 percent of people here are fully vaccinated. Three concerning strains of the virus have been detected in Maine. 

“This is a battle between vaccinations and the variants, and we want to make sure that the variants don’t spread,” Mills said.

Maine is set to join two dozen states that have made adults aged 16 and older eligible or will have by next Wednesday, according to The New York Times. Under Maine’s age-based system, about 80 percent of Mainers aged 70 and older have received at least one dose, as have roughly two-thirds of people in their 60s. Among Mainers in their 50s — who became eligible for the vaccine only eight days ago — nearly 2 out of every 5 people have been vaccinated.

Despite those figures, appointments have been slow to fill across the state in the past week. As of Thursday morning, Northern Light Health — which saw limited appointments snapped up in minutes earlier this year — had available spots within the next week at clinics in Bangor, Portland, South Portland, Dover-Foxcroft, Blue Hill, Presque Isle, Ellsworth and Fairfield.

Because Maine also prioritized health care workers, first responders, teachers and child care providers, a fraction of people under the age of 50 have already been vaccinated. But Thursday’s change still means more than 450,000 adults will become eligible next Wednesday, a significant volume that the state’s current sites will not be able to accommodate immediately.

Only the Pfizer vaccine is authorized for 16- and 17-year-olds, while all three vaccines are authorized for people aged 18 and older. Students attending college in Maine are eligible under state residency requirements, Department of Health and Human Services Commissioner Jeanne Lambrew said.

Providers are allowed to prioritize patients, including those with high-risk medical conditions, officials said Thursday. Mills noted the state planned to prioritize certain younger populations by routing vaccines to oncology practices and dialysis centers, among other providers.

The expansion of eligibility will also allow Maine to vaccinate younger people in jails and prisons, which have been a site of several major outbreaks of the virus, though state officials were noncommittal Thursday on the timeline, saying they would continue to work with the Department of Corrections — which is getting 200 new first doses next week — and county jails.