High stakes and big challenges await as the U.S. prepares to roll out vaccines against COVID-19, with front-line health care workers and vulnerable nursing home residents recommended as the top priority.

Doses could be on their way very soon. An independent advisory committee to the Food and Drug Administration on Thursday gave a green light to the first vaccine candidate, made by Pfizer in conjunction with the German company BioNTech—a recommendation expected to be approved by the agency within days. The committee is scheduled to consider a second candidate, made by Moderna, Dec. 17.

On tap is an initial stockpile of vaccines made during the approval process, with federal officials hoping to distribute at least 20 million doses by year’s end.

While that will go a long way toward reaching the top-priority groups—the nation’s 21 million health care workers and 3 million long-term care residents—there won’t be enough to inoculate everyone on Day One, or even the first week.

In Ohio, for example, the governor expects an initial delivery of 98,000 doses, with the state allocating 88,000 of those to long-term care facilities, said Pete Van Runkle, executive director of the Ohio Health Care Association, which represents long-term care facilities.

“It’s more than a drop in the bucket, but it’s not all that’s needed,” said Van Runkle, who estimated there are between 150,000 and 175,000 residents and staff members in long-term care centers in the state.

Consequently, the doses will be distributed in waves, with the centers and hospitals not chosen for the first wave getting them in the coming weeks, he said.

Facilities will have to divvy up the supplies to best address the needs of patients and employees.

For hospitals, first up are likely to be “workers with the greatest exposure” to the virus, said Anna Legreid Dopp, a senior director at the American Society of Health-System Pharmacists, a trade group representing more than 55,000 pharmacists who work for hospitals and health systems.

Then who? Perhaps those with personal medical conditions putting them at higher risk. And there may be other considerations specific to individual hospitals. What if, for example, only two people are trained to run a specialized treatment system in the ICU needed to care for patients seriously ill with COVID-19?

“Are they at the top of the list?” asked Dopp.

Nursing homes have a slightly different calculation because they have fewer employees than hospitals, said Van Runkle.

“It’s more a question of choosing which facilities” will get the initial doses, he said. “Once those are chosen, they’ll vaccinate everyone there [who consents], not pick and choose among people.”

Even so, there may be some selectivity because most nursing home employees are women and many are of child-bearing age. Because the vaccines have not yet been tested on pregnant women, those who are pregnant or breastfeeding may not be eligible in the initial rollout.

Which long-term care facilities get the vaccine first may come down to where they are located in relation to two large pharmacy chains: CVS and Walgreens.

In October, the federal government signed an agreement with CVS and Walgreens to store and administer the vaccines. Most long-term care facilities opted to join the partnership.

Under the agreement, the pharmacist teams will make at least three trips to each nursing home over a couple of months to administer the vaccines, which must be given in two doses, set several weeks apart.

One big hurdle in distributing the two vaccines seeking FDA approval is keeping them cold. The Pfizer vaccine is stored at around 94 degrees below zero, while the Moderna option is kept at minus 4 degrees. CVS expects to keep the vaccine at 1,100 locations around the country that have the required refrigeration technology, said Mike DeAngelis, senior director of corporate communications at CVS Health. From those hubs, teams of pharmacists and pharmacy technicians will take thawed doses of the vaccines to the long-term care facilities and administer them to staff and residents. About 30,000 homes have signed on with CVS for the clinics.

Walgreens expects to administer the vaccinations in more than 23,000 long-term care locations, according to a written statement.

While there’s no charge to the nursing homes or residents, Medicare will pay an administrative fee to CVS and Walgreens of $16.94 for the first shot and $28.39 for the second.

Yet there’s a flip side to the supply equation: What if no one wants to go first?

“That’s what keeps me up at night,” said Michael Wasserman, M.D., the immediate past president of the California Association of Long Term Care Medicine, a group of physicians, nurses, social workers and others who provide care to seniors.

That’s key because a good portion of America must be vaccinated to get to the much-sought-after “herd immunity,” in which most people are protected and the virus finds it difficult to spread.

“What if government and pharmacies do a great job in getting vaccine to the front door, then no one takes it?” Wasserman worries.

Nursing home residents are particularly vulnerable to COVID-19 and account for 40 percent of all reported deaths.

With COVID-positive test results on the rise in almost every state, vaccinating nursing home workers is crucial to protecting not only themselves, but also their patients.

That reality meets a reluctance among many front-line nursing home workers to take the vaccine, said Lori Porter, co-founder and CEO of the National Association of Health Care Assistants, which represents certified nursing assistants who work in long-term care.

Their distrust stems from many things, she said, including politicization around the vaccines, fueled by misinformation on social media.

Educational campaigns and personal endorsements from trusted organizations could help counter the falsehoods, she said. A nationwide event planned for next week by her organization will allow certified nursing assistants to ask questions directly of physician experts and hear from a panel of their peers.

“I’m asked 100 times a day if I’m going to be taking it,” said Porter, who definitely will, hoping to do so in a live webcast, to further convince her members it’s safe.

Despite the need to vaccinate staff to protect residents, Wasserman, a former regulator and nursing home executive, does not think mandates are appropriate for workers, many of whom are low-paid and people of color. “As a society, are we prepared to force this group of folks to get a brand-new vaccine?” he asked.

A better approach, he said, is the type of educational programs that Porter mentioned, so that workers can weigh the evidence and decide whether they want to get vaccinated.

Although employers may have the authority to mandate vaccination, many experts don’t think that policy will be widespread in the nursing home industry, given a shortage of workers and a fear of losing staffers who choose not to comply.

“I can tell you our members are not going to do that,” said Van Runkle, with the Ohio trade group. “If they were to try a mandate, some number of workers would say, ‘Sorry, this is the last straw. I’m leaving.’”

Instead of a mandate, Porter said, a few nursing homes are offering prizes or financial incentives—with at least one talking about offering a drawing for a new car among those who participate. Others, however, may take the opposite approach: ending supplemental hazard pay for workers who refuse.

As for residents, there is no debate. They will not get the vaccine unless they agree, often in writing, said Van Runkle.

For those with dementia or other health problems that prevent making such a decision, family members or others with legal authority must sign, which could slow down the vaccination process considerably.

“During a pandemic, it may be difficult to get hold of them or get their handwritten signature on a document,” said Van Runkle. “We’ve got to sort all this out in the next couple of weeks.”

KHN (Kaiser Health News) is a nonprofit news service covering health issues. It is an editorially independent program of KFF (Kaiser Family Foundation), which is not affiliated with Kaiser Permanente.