WASHINGTON — Federal health officials are expected as soon as Friday to expand access to COVID-19 booster shots to all American adults.

But some states aren’t waiting for a green light from D.C.

At least six states already have opened up eligibility for the boosters from Pfizer and Moderna beyond the categories specified by federal health agencies: anyone 65 and older, as well as those 18 to 64 with underlying health conditions or who are at higher risk because of their workplace.

Those states instead have told adult residents that they can seek another shot as long as they meet the other part of the federal rules—they must have received their second Pfizer or Moderna shot at least six months ago. (Anyone who received the one-dose shot from Johnson & Johnson already can receive an additional dose at least two months later under the federal rules.)

Maine became the latest state to expand booster eligibility on Wednesday, joining Colorado, California, New Mexico, West Virginia and Arkansas. New York City officials also have encouraged all adults who meet the timing requirements to seek another shot.

“With Maine and other New England states confronting a sustained surge, and with cold weather sending people indoors, we want to simplify the federal government’s complicated eligibility guidelines and make getting a booster shot as straightforward and easy as possible,” Maine Gov. Janet Mills said in Wednesday’s announcement.

Missouri is not among them, with state health officials continuing to follow federal recommendations that call for boosters for those  over 65, with an underlying medical condition or in a high risk profession. So far, just over 50 percent of all Missourians have completed vaccination.

As state officials did in Colorado and New Mexico, Maine officials are justifying the action by simply determining that all of their adult residents live or work in high-risk settings, in order to align with the federal rules.

“Because disease spread is so significant across Colorado, all Coloradans who are 18 years of age and older are at high risk and qualify for a booster shot,” stated the Nov. 10 executive order from Colorado Gov. Jared Polis.

Determining who exactly needs to receive a booster dose has been contentious.

Pfizer initially sought to offer booster doses to all American adults, and the Biden administration proclaimed in mid-August that it would launch a national booster campaign by Sept. 20.

But vaccine experts who advise the Food and Drug Administration and Centers for Disease Control and Prevention recommended narrower eligibility requirements, expressing skepticism that the available data shows a need for everyone to receive another dose. The CDC’s vaccine panel declined to recommend including employees at higher risk of exposure to the virus at their workplace, but the top CDC official added them back in the agency’s official guidance.

Polis has been critical of federal health officials, saying during an appearance Sunday on the CBS show “Face the Nation” that he has “been very frustrated with the convoluted messaging” from the CDC as well as the FDA.

During a press briefing Wednesday, Dr. Rochelle Walensky, who heads the CDC, sidestepped a question about the states that are forging ahead of her agency on booster-shot policy.

“FDA is currently evaluating data on the authorization of booster doses for all people over age 18,” she said. “As we’ve done before, CDC will quickly review the safety and effectiveness data and make recommendations as soon as we hear from FDA.”

Walensky added that those who are currently eligible for a booster shot are encouraged to seek one as soon as they can.

The New York Times has reported that the FDA is aiming to authorize booster doses of Pfizer’s  vaccine for all adults as early as Thursday. A CDC panel that crafts vaccine recommendations is scheduled to meet Friday.