Yet excitement over next week’s planned launch of a mass immunization program was tempered Friday by frustration over a late decision to exclude front line health workers from the first round — though many had already booked appointments.

Priority will go to people over 80 years old and to nursing home caregivers, and public health officials conceded that, even for those groups, demand could quickly outstrip supply in the early months. The 800,000 doses Britain expects to get this month “could be the only batch we receive for some time,” warned Chris Hopson, chief executive of NHS Providers.

Britain will be the first country to confront the challenges of rolling out a vaccine that uses revolutionary technology and requires extremely careful handling.

The United States isn’t far behind in its approval decision, and experience here could inform U.S. efforts — though the United Kingdom’s universal health-care system allows a more centralized approach.

The chief operations officer for Operation Warp Speed, Army Gen. Gustave Perna, told reporters this week the federal government plans to distribute 6.4 million doses of Pfizer’s vaccine to states within 24 hours after an expected emergency-use authorization by the Food and Drug Administration.

While the United States, like Britain, may need time to ramp up, the White House vaccine team predicted 100 million Americans could be immunized by the end of February.

A Centers for Disease Control and Prevention advisory panel on Tuesday voted to recommend prioritizing residents of long-term care homes and health-care workers. That’s in keeping with the priority lists in many countries around the world. But Britain shocked its National Health Service medical workers Thursday evening by revealing that, contrary to long-held assumptions, they would not be among the first to get an injection.

Frontline nurses and doctors have been regularly hailed as national heroes in Britain. In the early months of the cresting pandemic, citizens filled the streets banging pots and pans, blowing horns and clapping in weekly displays of appreciation for their courage.

But now, along with much of the country, they will be expected to wait.

Mike Adams, director for England at the Royal College of Nursing, said that in the past few weeks, “messaging from politicians has been focused on ‘the NHS staff will get it,’ and so some of the narrative from politicians has been unhelpful in raising expectations.”

Adams told The Washington Post, “We want to see our members have access to it for their own safety and to prevent further outbreaks in the areas they are working, but we appreciate that with limited supply of vaccine, you understand why the most vulnerable are being prioritized. But the confusion is the most unhelpful part.”

Rachel Luby is nurse specializing in mental health at NHS in London. “For me the issue is not that those aged over 80 having the vaccination before I do. I have seen first hand, in my grandmother, how loss of routine and activity has impacted her, and she has gone from an active, healthy woman to someone who is now quite frail,” Luby said, adding that it is also smart to form a “protective ring” around nursing homes by vaccinating care givers there.

Luby said, “What does affect me is the message from the government, time and again, that they simply do not care about the lives of those who work in the NHS. They ‘clapped for us and then they slapped us’ is the way that I and many frontline colleagues feel.”

She said, “I feel for those staff who had got their hopes up that they would be getting 'the tools to do their job,’ because I do see the vaccine as being akin to that,” a tool to do the job.

Instead of ICU nurses, ventilator specialists and emergency room physicians, NHS officials and vaccine task force members said they wanted to prioritize the elderly and nursing home caregivers — because the highest mortality and the largest number of hospitalizations have come from that age group and sector.

Unfortunately, however, NHS officials conceded they do not yet have a protocol nor approval from drug regulators to offer Pfizer injections within nursing homes.

The vaccine, developed by the German company BioNTech and manufactured by Pfizer, is built on tiny bits of messenger RNA, which encourage the body to produce antibodies to repel the spike protein on the surface of the coronavirus. RNA vaccines need to be stored and shipped at seriously cold, sub-Antarctic temperatures of minus 75 Celsius, and so they require special handling.

British regulators, in granting emergency approval for the Pfizer vaccine, said it cannot be moved more than four times and that the trays of 975 doses cannot be split apart — and nursing homes are typically smaller than that.

“It’s not like taking a six pack of yogurt out of your home fridge, breaking it up on the kitchen work top, putting one in your bag, taking it to work and then storing it in the work fridge,” Hopson said.

So, while the NHS figures out how to get into nursing homes with this or another vaccine, the first jabs will be injected at one of the 50 hospitals serving an immunization hubs. Next year, the government plans to open mass immunization centers in conference centers, sport arenas, and schools.

Overall, Britain has ordered 40 million doses of the Pfizer vaccine, enough to vaccinate 20 million people, as each requires two shots, three weeks apart.

Business minister Alok Sharma told Sky News on Friday that he hoped the country would get “some millions” of doses from Pfizer this month, “but, of course, what we also always said is that the vast majority of this vaccination program will take place in the new year.”

The initial 800,000 doses promised from Pfizer won’t go far to cover the 3.2 million Brits aged 80 and above and the at least 300,000 caregivers working in nursing homes.

All of those people will be in line before the more than 1.4 million NHS workers.

Chaand Nagpaul, chair of the British Medical Association, the main doctors union, said that with limited supplies, it was important that those deemed most at risk were prioritized, but he criticized the government’s inconsistent messaging.

“During the first wave, we saw far too many health- and social-care workers become incredibly sick with covid — with many tragically dying — and therefore those working on the front line need to be given the opportunity to get protected early,” Nagpaul said.

“It’s crucial now that there’s absolute consistency and clarity, as more vaccines become available, for both the public and health care staff about when and where they can expect to be vaccinated,” he said.

Paul Hunter, a professor in medicine at the University of East Anglia, said the deployment will be a “big challenge,” but added that U.K. hospitals and labs were well equipped for handling samples that need low temperatures, including using liquid nitrogen and dry ice.

He said if the aim is to reduce the death toll, it made sense to prioritize nursing homes, which were hit “really badly” in the first wave.

After that, he said, the next on the list could be health care workers, “not only because they’re more at risk themselves, but they care for a lot of the people in the extremely vulnerable older age group.”

This is also important if there isn’t widespread uptake in those over 80 years old.

“If you target the upper 80s, and if they don’t take it up like you hoped, then the next best thing is to vaccinate people who come into close contact with them, which will be the health-care workers.”