WASHINGTON (NYTIMES) - United States state health officials on Friday (Sept 24) rushed to roll out campaigns to provide coronavirus booster shots for millions of vulnerable people who received the Pfizer-BioNTech vaccine and to help a confused public understand who qualifies for the extra shots.

Among their challenges: making sure that recipients of the Moderna and Johnson & Johnson vaccines know that they are not yet eligible for boosters; reaching isolated elderly people; and informing younger adults with medical conditions or jobs that place them at higher risk that they might be eligible under the broad federal rules.

"Those of us overseeing vaccine roll-outs don't have a clear idea of what to do," said Dr Clay Marsh, West Virginia's Covid-19 czar.

In his state, pharmacies sent staff members into the largest nursing homes on Friday to administer booster doses.

In Vermont, health officials opened booster shot appointments to people 80 and older on Friday, and said many other eligible people could get them starting next week. But the state said it was waiting for clarity from the Centres for Disease Control and Prevention (CDC) on which workers and medical conditions would qualify.

In virus-battered North Dakota, officials struggling to make sense of the federal guidance delayed a broad booster rollout until next week, with a focus on reaching elderly residents and those in long-term care settings, said Ms Kylie Hall, an adviser to the state's Health Department.

Across the country, vaccine providers are facing the reality that many more people became eligible for boosters after CDC director Rochelle Walensky overruled her expert committee early on Friday. She said people at greater risk of exposure to the virus "because of occupational or institutional setting" would qualify, opening up boosters to millions of people her advisory committee had left out.

People 65 and older and residents of long-term care facilities and adults who have certain medical conditions also qualify for the boosters.

After Dr Walensky's announcement, US President Joe Biden said 20 million people could get boosters immediately because they had gotten their second Pfizer-BioNTech shot at least six months ago. In all, he said, 60 million people will be eligible for a Pfizer-BioNTech booster over the coming months.

"If you got the Pfizer vaccine in January, February, March of this year and you're over 65 years of age, go get the booster," Mr Biden said. "Or if you have a medical condition like diabetes, or you're a front-line worker, like a healthcare worker or a teacher, you can get a free booster now."

Still, people such as Mr Don Driscoll remain wary of coronavirus vaccines. Mr Driscoll, 38, who lives in suburban Pittsburgh, has been derided by friends for not getting vaccinated. But he is not comfortable yet, he said, because of the lack of consensus about the shots.

With exasperation, he pointed to the ping-ponging of contradictory booster advice in the past few weeks from federal health authorities and the White House, which has only reinforced his apprehension.

"I feel that everything that has been happening is justifying people's hesitancy," he said.

State and federal officials said the booster program would look much different than earlier coronavirus vaccination drives, which relied heavily on mass inoculation sites at sports stadiums and convention centres. Instead, pharmacies, primary care physicians and smaller vaccination clinics that have become accustomed to offering shots will deliver boosters.

"That track has been laid, and we can continue to move the booster train, if you will, right down that same set of tracks," Ms Karen Timberlake, secretary designee of Wisconsin's Department of Health Services, told reporters this week.

Pharmacies are providing roughly 70 per cent of coronavirus vaccinations as of this week, according to the CDC. Mr Biden said booster shots would be available at 80,000 locations around the country, including more than 40,000 pharmacies.

CVS said on Friday that its pharmacies were ready to provide booster shots and would rely on customers to "self-attest" regarding their eligibility.

Administration officials were hoping that the CDC's recommendations would bring some closure to a dissent-filled month of preparing for a booster campaign. The CDC held calls with state health departments and pharmacies Friday to discuss how to roll out the shots, and the White House briefed governors on the topic.

Dr Mark Levine, Vermont's top health official, pointed to one potential challenge for his state: Many teachers there received the single-dose Johnson & Johnson vaccine, for which booster shots are not yet authorised, leaving them in limbo. A booster program with only Pfizer-BioNTech's vaccine, he said, will require "a lot more messaging and communication".

In West Virginia, which has one of the highest daily average case rates in the country, Marsh said many who most needed extra shots would be left waiting. More isolated nursing homes in the state received the Moderna vaccine, he said.

So did rural communities in Alaska, said Dr Anne Zink, the state's top health official. But Marsh praised the CDC's allowance of booster shots for health workers, saying it could help sustain badly strained hospitals in his state.

Dr Zink said the early morning CDC decision had provided needed clarity about how to advise vaccine providers.

"It was the bow at the end," she said.

As a practical matter, the official recommendations were unlikely to deter millions of Americans who might not be eligible yet from pursuing booster doses, by claiming medical conditions or weakened immune systems, by asking doctors to prescribe the vaccine off label or by finding a pharmacist willing to give them one. The CDC said on Thursday that millions of Americans had already received an extra shot.

Asked on Friday how officials might prevent ineligible people from getting a shot, Dr Walensky said providers would have to rely on people giving their word.

Mr Winthrop Gardner, of Durham, North Carolina, said that several weeks ago, his 65-year-old wife, a hospital administrator, was growing anxious; her second Pfizer-BioNTech shot had been nine months earlier. So, Mr Gardner said, she decided to take matters into her own hands.

On an online pharmacy portal, she read a list of medical conditions that would render her eligible, some of which she did not even recognise. The last option read: "I don't know."

Because she is scrupulously honest, he said, she checked that box. And immediately got her booster appointment.