State health officials are bracing for confusion as they manage expectations about coronavirus boosters that President Biden announced last month would be widely available to adults this week.

The two federal agencies that determine who should get a booster — the Food and Drug Administration and Centers for Disease Control and Prevention — are not expected to issue decisions until later this week. But in last month’s announcement, Biden and his top health advisers set the week of Sept. 20 as the start for a booster rollout that would make third shots available to adults eight months after completing their original two-shot regimen.

Even though federal officials emphasized that the plan required FDA and CDC approval, specifying a date has meant “the expectation has been set by the administration that we now have to manage,” said Michael Fraser, executive director of the Association of State and Territorial Health Officials.

“It puts the states in a difficult position,” Fraser said in an interview Saturday.

During a call Friday, state health officials spoke of the “difficulty in messaging, difficulty in telling people to be patient yet again — yet another challenging and confusing message that doesn’t universally apply,” Fraser said.

Some states, such as Virginia, anticipating the interest in boosters, have posted online notices urging residents to be patient and to wait for further guidance once final recommendations have been provided by the federal government.

In some states, “there will be the expectation that there will be boosters” on Monday, said Anne Zink, Alaska’s chief medical officer.

“We’ve been trying to message for the past few weeks that we really need to wait on the FDA and CDC,” Zink said in an interview Sunday. “But as we’ve all experienced, this pandemic messaging can be challenging, and our platform is definitely not as big as the White House’s.”

In parts of the Northeast, in states with large elderly populations and high demand for boosters, “we just need to be ready for an operational plan” if the CDC advisory committee endorses a third Pfizer dose, said Nirav Shah, director of Maine’s Center for Disease Control and Prevention. He said highly motivated health-care consumers have been emailing him about when and where they can get a booster.

On Friday, an FDA advisory panel voted to recommend that the agency authorize a booster shot of the Pfizer-BioNTech coronavirus vaccine for people 65 years and older and for anyone at risk for severe illness six months after completing the original two-shot regimen. The recommendation was far narrower than what top officials in the Biden administration had wanted. The panel decided there is not enough evidence of the need or benefit for a broader population to receive booster shots.

The panel’s recommendation is not binding, and the FDA is expected to announce a decision within days. Following that, the CDC’s Advisory Committee on Immunization Practices is scheduled to meet Wednesday and Thursday to make further recommendations on who should get a third Pfizer shot.

The focus on a Pfizer booster presents real-world challenges for front-line health officials. About 81 million people have received shots made by Moderna and Johnson & Johnson, but their eligibility for a booster was not addressed during the FDA advisory committee meeting and may not be decided for weeks.

On Sunday, Anthony S. Fauci, chief medical adviser to the White House covid-19 response, said data for an extra shot of the Moderna and Johnson & Johnson vaccines is a few weeks away from being presented to the FDA.

“We’re working on that right now, to get the data to the FDA so they can examine it and make a determination about the boosters for those people,” Fauci said on NBC’s “Meet the Press.” “They’re not being left behind by any means.”

The CDC cautioned state health officials last week not to give booster shots until the FDA and CDC take action. In an email sent to states Thursday, the CDC wrote: “As we have informed you previously, the Administration has been making preparations to begin a COVID-19 booster shot rollout as early as the week of September 20. … Any implementation of booster programs should begin after FDA takes a regulatory action and ACIP and CDC make clinical recommendations for use.”

That is forcing health officials to make difficult decisions.

“Our hospitals here in Alaska and many hospitals in the country are really facing unprecedented choices and decisions about care and trying to weigh the risk-benefit of things like a booster shot versus, you know, waiting,” Zink said. “And while I appreciate the comments of waiting, it’s challenging given the threat of covid right now.”

In Colorado, health systems are considering or moving forward with booster dosing. Zink said such actions reflect that “they cannot afford staff to be out even for a short period of time, even if they’re mildly ill or not very ill, because they’re so desperately needing to keep staffing up.”

Nursing homes and other long-term-care facilities are a priority for vaccination because of the devastating waves of infection and deaths in earlier phases of the pandemic. But in some nursing homes, half the residents were vaccinated with the Pfizer product, and the rest received Moderna.

“The states that have long-term-care facilities that went through with Moderna, they are sort of in limbo,” said Claire Hannan, executive director of the Association of Immunization Managers. “They’re planning both ways. They may need to give Pfizer as the booster.”

Adding to the confusion: Federal officials have already approved Pfizer and Moderna boosters for people with weakened immune systems, such as cancer patients and transplant recipients.

Rural parts of the country also relied more heavily on the Moderna vaccine, which comes in smaller batches than Pfizer and has less demanding storage requirements, and the one-shot Johnson & Johnson product. In the remote community of Unalaska, on an Aleutian island off mainland Alaska, an employee at the main health clinic asked Zink last week whether staffers could give booster doses of Moderna about to expire at the end of September.

Everyone who could have had their shot has already been vaccinated, a clinic staff member told Zink. “Their vulnerable populations are desperate for a booster dose, particularly when they’re watching the clock on this vaccine start to expire,” Zink recalled. She said the person asked, “Can we please give a booster dose to at least those who are willing to accept the risk and who are at high risk, such as health-care workers and the elderly?”

“Those are the kinds of real-world questions that I think we’re all struggling with in this space of looking for the science and data but then also looking at the real-world questions and trying to apply it clinically as well as logistically and practically throughout the state,” Zink said.