In this March 2, 2021, file photo, a pharmacy technician loads a syringe with Pfizer's COVID-19 vaccine at a mass vaccination site at the Portland Expo in Portland. Credit: Robert F. Bukaty / AP

Accessibility of mix-and-match COVID-19 vaccine boosters was uneven in Maine on Friday, the first day they were made available, with some chains providing them and others set to begin next week.

The U.S. Centers for Disease Control and Prevention approved booster shots for Moderna and Johnson & Johnson recipients on Thursday, also saying anyone who is eligible for another dose can get a different vaccine than the one they got initially. All adults who got the Johnson & Johnson shot can get a booster of their choice two months or more after their initial shot, while boosters to Moderna and Pfizer are authorized for seniors and high-risk adults.

The addition of more boosters could be crucial to reducing harm from the virus in the long run after stubbornly high COVID-19 cases driven by the delta variant over the summer have begun to wane. Not all providers were immediately offering all eligible boosters, although that will likely change soon as they align their policies with the new federal changes.

They are recommended primarily for people who are over 65 years old and people aged 50-64 who have underlying medical conditions, although people of any age with certain medical conditions or increased exposure to the virus are also advised to get an additional shot based on their risk. Those people are typically more vulnerable to the virus, although the surge in new cases has primarily been among unvaccinated people.

Booster recommendations vary depending on when you were vaccinated. The U.S. Centers for Disease Control and Prevention recommends eligible people who got Pfizer and Moderna vaccines for their initial doses get boosters after six months.

The Johnson & Johnson window is tighter because the one-dose vaccine had a lower efficacy rate than the other two, though initial data show that a second dose of that vaccine raises protection against serious illness to the same level as the two-dose vaccines. Mix-and-match boosters were allowed after preliminary data showed that people who got the Johnson & Johnson vaccine and got a Moderna or Pfizer booster may have even higher antibody levels.

Two of Maine’s biggest hospital systems, Portland-based MaineHealth and Bangor-based Northern Light Eastern Maine Medical Center, expect to have mix-and-match boosters available by next week. John Porter, a spokesperson for MaineHealth, said people can begin scheduling appointments for next week — but unlike when vaccines were extremely plentiful, not every location is set up for vaccines, and people should call ahead to see if a location has the booster they want instead of just walking in.

Northern Light is expected to offer all three boosters by next Monday, the network said in a news release. The system is still updating its scheduling system to accommodate people who want a different shot than the original one they received, and an update on that is expected next week. The system’s online platform or phone number can be used to schedule a third dose.

But MaineGeneral Health in Augusta is waiting for a final sign-off from the U.S. Centers for Disease Control and Prevention — the agency offered guidance on the Moderna and Johnson & Johnson boosters Thursday — and the state before offering Moderna and Johnson & Johnson boosters, said spokesperson Nicole McSweeney. It is offering Pfizer boosters and will offer mixed boosters as soon as it gets information on how to roll out the Moderna and Johnson & Johnson vaccines from the state.

Among big pharmacies, availability for mixed boosters varies. Walmart announced Friday boosters of all three doses are currently available. Walgreens is also making all three doses available. Both chains allow people to schedule those doses online. But Hannaford appears to be only offering Moderna and Pfizer boosters for people who got those shots initially.

Other locations may offer boosters, but it’s recommended to check in with them first. The Maine Center for Disease Control and Prevention had not updated its website on Friday to reflect where Moderna or Johnson & Johnson vaccines may be available, but gave instructions to providers last Friday on how to order Moderna boosters ahead of their authorization.