Now comes the hardest part: Getting a coronavirus vaccine from the loading dock to the upper arm

Riverside Health System in Virginia has ordered a specialized freezer for each of its five hospitals to keep precious vials of coronavirus vaccine as cold as a deep Antarctic freeze.

Public health officials in Nashville and Baltimore are revamping routine flu clinics to test delivery methods for coronavirus vaccinations.

And in Maine, top health official Nirav Shah spends sleepless nights devising drive-through immunization facilities where vaccinators won’t have to wear winter parkas in addition to their personal protective gear.

Shah’s solution? Fire stations and carwashes.

Those venues are heated “so you have shelter from the snow and cold,” he said. “We haven’t inked any of those agreements yet, but that’s where our head is at.”

Buoyed by promising results from major clinical trials of three coronavirus vaccines, public health officials are preparing for the daunting task ahead of delivering those shots to tens of millions of Americans. On Monday, a third pharmaceutical company announced positive results from late-stage trials of a coronavirus vaccine, saying that its candidate is up to 90 percent effective.

The vaccines need to be distributed across 50 states, plus U.S. territories, that have different demographics and shifting needs. The leading products must be stored at different temperatures and have different minimum orders, with each requiring two shots but at different intervals.

Complicating matters: A final decision on who is eligible to get the early doses must wait for a federal advisory group’s recommendations. That can’t happen until regulators authorize the new vaccines. And once set in motion, the distribution - from loading dock to upper arm - has to be accomplished equitably and with as few handoffs as possible because it’s all being done amid a pandemic.

The stakes are enormous. The massive undertaking to immunize most of the population requires extraordinary communication, planning and coordination. Federal, state and local officials are working with hospitals and pharmacies, suppliers of dry ice, gloves and vials, and carriers such as UPS and FedEx. A successful operation could transform the health and economic well-being of society, in the United States and overseas.

“There are a million moving parts,” said Bruce Gellin, president of global immunization at the Sabin Vaccine Institute. “The system is complex to start with, [and] it is being modified to mount an immunization campaign of historic proportions,” he said, warning that while “expectations are sky high,” there are pitfalls at every step.

Officials are wrestling with how to ensure vulnerable populations receive the vaccine. Almost certainly at the front of the line: about 21 million front-line health-care workers. Next up are likely to be other essential workers, many of whom come from Black, Latino and Asian communities hard hit because of socioeconomic factors. Many can’t work from home, don’t have transportation and live in crowded housing.

“It’s like treating an individual patient while rebuilding the entire health-care system,” said Alfred Sommer, former dean of the Johns Hopkins Bloomberg School of Public Health, who was part of the team that vanquished smallpox four decades ago. Challenges will crop up, he said, such as immunizing disadvantaged communities. “Even with special outreach programs, it will not be easy with the vaccines ready for approval.”

Further complicating the logistics: the continued intrusion of politics. The Trump administration has not given information about vaccine distribution to the Biden transition team, President-elect Joe Biden’s chief of staff, Ron Klain, said in an interview Sunday on ABC’s “This Week,” adding to the potential for disruption.

“I have faith that the incoming administration will not completely upend the thousands of man and woman hours of work we’ve put in,” said Cindy Williams, vice president of the Riverside Health System and a member of Virginia’s coronavirus advisory committee. “Creating additional chaos as we’re managing this is really a bad idea.”

Once the vaccines are authorized by the Food and Drug Administration, doses will be allocated to each state according to population, with some held in reserve in case of loss or theft. Within 24 hours of FDA action, doses will be “prepositioned” at key sites designated by each state where vaccines will be administered to the first priority groups.

U.S. government officials anticipate having 40 million doses of vaccines from pharmaceutical giant Pfizer and biotech firm Moderna by the end of the year, enough to vaccinate 20 million people, a small fraction of the U.S. population of 330 million. (The United States will receive about half of Pfizer’s 50 million doses globally.) Government officials say it will be April before most people could get vaccinated.

The good news from AstraZeneca, manufacturer of the third vaccine, which is easier to store and transport, means the company will also apply for regulatory approval in the United States.

» READ MORE: AstraZeneca: COVID-19 vaccine shown to be ‘highly effective’, affordable, and easily transportable

Americans will receive coronavirus vaccines free. The federal government is paying for much of the delivery and vaccine administration costs. But state officials are asking Congress for at least $8 billion for vaccination efforts; to date, $200 million in federal funds has been sent to state, territorial and local jurisdictions.

The vials will be sent first to large hospitals and other sites where mass immunization clinics can take place. But even that first step presents daunting travel, storage and handling requirements.

The Pfizer vaccine will be shipped to sites selected by states in GPS-tracked, suitcase-sized “shippers” with 50 pounds of dry ice pellets, and must be kept at minus-70 Celsius. Upon arrival, the dry ice must be refreshed, or the vials of vaccine must be transferred to ultralow-temperature freezers. The specifications are exacting if the vials stay in the shippers: The container cannot be opened more than twice a day, the dry ice must be replenished every five days, and the contents must be used within 15 days. The vials can stay at refrigerator temperature for five days before their contents degrade.

The Moderna vaccine is less demanding, with a storage temperature of minus-20 Celsius, which is the same for many medications.

The shipments need to be coordinated with kits of syringes, needles, face masks and other ancillary supplies.

From there, every state, territory and each of six major metropolitan areas is responsible for its own deployments. States are in varying stages of preparation. Many have designated large hospital systems to be the first places to receive vaccine. Maine, for example, has chosen five hospitals with ultracold freezers to receive its first doses, and each has a plan to reach into the community. But just in case, the state bought an ultracold freezer for its public health emergency warehouse that can store more than 200,000 doses.

Maine has held meetings with transportation officials and the National Guard to work through worst-case scenarios, Shah said. If there’s a flood or loss of power, a backup generator for the freezer would kick in. If shots are transported during a blizzard, the vaccine convoy could follow 30 minutes behind a salt truck.

The Centers for Disease Control and Prevention has told states they don’t need to buy specialized freezers because immunizations in the earliest phases will focus on sites that can vaccinate as many people as possible and will be able to handle the cold chain requirements, even without freezers.

But at the Henry Ford Health System in Detroit, Northwell Health in New York and Riverside in Virginia, officials bought them anyway, executives said on a conference call Thursday about vaccine distribution organized by Premier, the group purchasing organization and supply consultancy for 4,100 hospitals. The executives’ assumption was that early public vaccination clinics will be most efficiently done on the campuses of hospitals with ultracold freezers.

Among them is Riverside Shore Memorial Hospital on Virginia’s Eastern Shore, a medically underserved and rural community that includes poultry and agricultural workers who did not have health insurance until the state recently expanded Medicaid, said Williams, of Riverside Health. It is one of three major health-care providers for the community, and the only one with an ultracold freezer.

Clinicians will need to be trained to administer the vaccines, which have different protocols. The Pfizer version must be diluted before the shot is given - inverting the vial 10 times “gently,” according to the Pfizer instructions. In contrast, the Moderna vaccine does not require on-site mixing and should not be shaken.

To start with, vaccination efforts may favor urban areas. That’s because the vaccines will arrive in big batches: For Pfizer, the minimum order is 975 doses. Moderna’s smallest batch is 100 doses.

In Alaska, “you’re not going to have 900 people within 1,000 square miles,” said Danny Staley, a senior vice president at the Association of State and Territorial Health Officials. “You’re wanting to do that at a mass vaccination clinic, where we know people can use it so we don’t waste it,” he said.

“The most disadvantaging issue is the minimum order,” said Ann Lewandowski, program manager for the Southern Wisconsin Immunization Consortium, a group of 42 rural hospitals in Wisconsin. None has the resources to purchase a special freezer, which can cost $12,000 to $15,000 and might be needed for only a year until vaccines are developed that don’t require such frigid temperatures.

Identifying enough health-care workers to be immunized is also challenging for rural hospitals that may have only 20 nurses and 20 doctors. “You would need to reach out to pharmacists, reach out to dentists and all these other professionals, but 975 is really an impossible goal,” Lewandowski said.

On a recent call, a Pfizer representative told Lewandowski the company hopes to send out smaller batches of 125 doses by April. But even that creates logistical challenges because the vials need to be coordinated with the ancillary kits, which are equipped for 100 doses.

Health-care personnel from rural hospitals may have to drive to get their shots at larger hubs in Madison, Milwaukee or Eau Claire, Lewandowski said. That could pose a barrier for staffers already stretched thin caring for patients with covid-19, the illness caused by the coronavirus.

“These are health-care workers who are taking risks to serve the state in our time of need, and it’s not fair to discriminate against them simply because they live in a geographically challenged place,” Lewandowski said.

A Pfizer spokeswoman said the company is working on a smaller pack size that will be ready the first three months of 2021

Final recommendations on who gets the first shots will come from an independent committee on immunizations that advises the CDC. There is broad agreement that health-care workers will be first, and will include clinicians, custodial staff, home health aides, pharmacists, paramedics and staff in long-term care facilities, according to meetings of the Advisory Committee on Immunization Practices. That first group may also include about three million long-term care residents.

Jose Romero, a pediatric infectious-diseases specialist who chairs the immunization panel, said “essential workers” are likely to be high on the list. That might include people who stock supermarket shelves or pick vegetables, many of whom belong to communities of color devastated by covid-19.

“That is part of the equity question we are trying to solve,” Romero said.

That assumes priority groups are willing to take the first shots. Health officials say they are increasingly worried about staffers who say they won’t take the vaccine, according to internal surveys and conversations with clinicians.

“When it comes to this vaccine, what I’m hearing from colleagues . . . is that their confidence is lacking,” Pamela G. Rockwell, a physician representing the American Academy of Family Physicians, said during last month’s meeting of the federal immunization advisory committee.

“I’m already won over,” she said. “We need to win over a lot of primary care physicians . . . We need to do this right and get our patients convinced that this is safe so we can save our country.”

Federal health officials are also concerned.

“I am worried that people are going to equate the complicated storage and handling as somehow more reason to be hesitant about the vaccine, when in fact, it has nothing to do with how well the vaccines work,” said a senior federal health official involved in distribution with the Defense Department and private industry. The official spoke on the condition of anonymity because they were not authorized to speak publicly on the record.

At Riverside, a survey last month of about 1,000 employees, most in nursing and administrative positions, found about a third said they would take the vaccine, another third said they would not, and the remainder wanted more data on safety and efficacy. A separate poll of physicians found nearly half would not take the vaccine. The surveys were conducted before reports about the vaccines’ effectiveness, and acceptance is likely to increase, said Riverside’s Williams.

Patients will be more likely to be vaccinated if they ask their doctors if they’re willing to be vaccinated and the physician says yes, she said.

Saad B. Omer, an epidemiologist and infectious-diseases expert who directs the Yale Institute for Global Health, has done extensive studies about the political and social factors influencing trust in vaccines. What he sees now is not “your run-of-the-mill vaccine hesitancy.” President Donald Trump’s actions fueled mistrust in science, he said.

But health-care personnel can be persuaded. Strong endorsements from a trusted person, such as Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases, can make a huge difference, according to a study Omer conducted recently.

Experts who study vaccine hesitancy say promotional campaigns that use social media and increase community engagement with trusted leaders will be key to encouraging use of a new vaccine.

Adam Abadir, director of communications at the Baltimore City Health Department, said the city’s health officials had been using routine flu clinics to hone strategies such as tailored social media campaigns and outreach through pastors and other trusted community members.

“We now have partners in place who can deliver the messages,” Abadir said, even though he doesn’t yet know what those messages will say.

In Nashville, the annual “Flulapalooza” mass vaccination event at Vanderbilt University Medical Center - last year, they managed 15,000 shots on site in one day - was modified as Flula-2-uza to test strategies for the coronavirus, which may involve reversing their strategy and venturing out to remote workers.

» READ MORE: Why COVID-19 vaccines seem to work better than expected

The new vaccines are likely to produce more unpleasant side-effects than a flu shot, potentially leading recipients to need a day or two off work.

“Any group of individuals that work together, we can’t vaccinate them all at the same time,” said Thomas Talbot, chief hospital epidemiologist at Vanderbilt, which will likely be among the first sites to receive the Pfizer vaccine and is looking at how to stagger immunizations to minimize the impact on departments.

In Baltimore, a mobile flu clinic in a predominantly Latino community drew more than 150 people on a recent stormy morning to a school parking lot, where a team of Spanish-speaking officials were working with next year in mind.

Drive-through vaccination isn’t viable for people in the city who lack transportation, said Rebecca Dineen, assistant commissioner for the city’s Bureau of Maternal and Child Health. So the health department is pushing hard to foster links in public housing and with neighborhood leaders who will be key to coronavirus distribution.

“You don’t need a fancy innovative approach,” Dineen said. “A lot of it is really knowing your people.”

Shah, in Maine, is hoping that beyond cultivating relationships with pharmacies and physicians offices, fire stations and carwashes will be all the innovation he needs.

“We think the fire departments are a pretty good source for sites because there are so many, many small towns in Maine,” he said.

EMS clinicians can be vaccinators there or at carwashes.

“People trust them,” he said. “And trust matters a lot.”