LONDON >> A nurse rolled up 90-year-old Margaret Keenan’s sleeve and administered a shot watched round the world -– the first jab in the U.K.’s COVID-19 vaccination program kicking off an unprecedented global effort to try to end a pandemic that has killed 1.5 million people.

Keenan, a retired shop clerk from Northern Ireland who celebrates her birthday next week, was at the front of the line at University Hospital Coventry to receive the vaccine that was approved by British regulators last week.

The U.K. is the first Western country to deliver a broadly tested and independently reviewed vaccine to the general public. The COVID-19 shot was developed by U.S. drugmaker Pfizer and Germany’s BioNTech. U.S. and European Union regulators may approve it in the coming days or weeks.

“All done?” Keenan asked nurse May Parsons. “All done,” came the reply, as hospital staff broke into applause and also clapped for her as she was wheeled down a corridor.

“I feel so privileged to be the first person vaccinated against COVID-19,” said Keenan, who wore a surgical mask and a blue “Merry Christmas” T-shirt with a cartoon penguin in a Santa hat. “It’s the best early birthday present I could wish for because it means I can finally look forward to spending time with my family and friends in the New Year after being on my own for most of the year.”

The second injection, in a fitting bit of drama, went to an 81-year-old man named William Shakespeare from Warwickshire, the county where the bard was born.

The fanfare was good cheer to the nation, if but for a moment. Authorities warned that the vaccination campaign would take many months, meaning painful restrictions that have disrupted daily life and punished the economy are likely to continue until spring. The U.K. has seen over 61,000 deaths in the pandemic — more than any other country in Europe — and has recorded more than 1.7 million confirmed cases.

“This really feels like the beginning of the end,″ said Stephen Powis, medical director for the National Health Service in England. “It’s been a really dreadful year, 2020 — all those things that we are so used to, meeting friends and family, going to the cinema, have been disrupted. We can get those back. Not tomorrow. Not next week. Not next month. But in the months to come.″

But it is important beyond these shores. Britain’s program is likely to provide lessons for other countries as they prepare for the unprecedented task of vaccinating billions.

On Saturday, Russia began vaccinations with its Sputnik V vaccine, and China has also begun giving its own domestically made shots to its citizens and selling them abroad. But those are being viewed differently because neither countries’ vaccines have finished the late-stage trials scientists consider essential for proving a serum is safe and effective.

Other vaccines are also being reviewed by regulators around the world, including a collaboration between Oxford University and drugmaker AstraZeneca and one developed by U.S. biotechnology company Moderna.

Documents released by U.S. regulators Tuesday confirmed that Pfizer’s vaccine was strongly protective against COVID-19 and appeared safe. New results on a possible vaccine from Oxford University and drugmaker AstraZeneca suggest it is safe and about 70% effective, according to early test results from Britain and Brazil. But that report, in the medical journal Lancet, showed that questions remain about how well it helps protect those over 55.

British regulators approved the Pfizer shot Dec. 2, and the country has received 800,000 doses, enough to vaccinate 400,000 people. The first shots are going to people over 80 who are either hospitalized or already have outpatient appointments scheduled, along with nursing home workers and vaccination staff.

Others must wait, and health officials have said that those who are most at risk from the virus will be vaccinated in the early stages. For most people, it will be next year before there is enough vaccine to expand the program.

U.K. health officials have worked for months to adapt a system geared toward vaccinating groups like school children and pregnant women into one that can rapidly reach much of the population.

Questions arose about when the country’s most prominent senior couple — Queen Elizabeth II, 94, and her husband, Prince Philip, 99 — would get the vaccine and whether it would happen on camera.

Foreign Secretary Dominic Raab appeared nonplussed when he was asked about it by NBC.

“I’m not sure whether they’d do it on camera,’’ Raab said. “But I’m sure arrangements will be made according to the phased approach that I set out, and like any family, they would have felt the pressures and all the worries that surround this pandemic as well.’’

The 800,000 doses are only a fraction of what is needed in the U.K. The government is targeting more than 25 million people, or about 40% of the population, in the first phase of its vaccination program, which gives first priority to those at highest risk from the virus.

The program will be expanded when supply increases, with the vaccine offered roughly on the basis of age groups, starting with the oldest. Britain plans to offer vaccines to everyone over the age of 50, as well as younger adults with health conditions that put them at greater risk.

In England, the vaccine is being delivered to 50 hospital hubs in the first wave of the program, with more hospitals expected to offer it as the rollout ramps up. Northern Ireland, Scotland and Wales are making their own plans under the U.K.’s system of devolved administration.

Logistical issues are slowing the distribution of the Pfizer vaccine because it has to be stored at minus-70 degrees Celsius (minus-94 degrees Fahrenheit). Authorities are focusing on large-scale distribution points because each package of vaccine contains 975 doses and they don’t want any to be wasted.

The U.K. has agreed to buy more than 350 million doses from seven different producers. Governments around the world are making agreements with multiple developers to ensure they lock in delivery of the products that are ultimately approved for widespread use.

All these logistical challenges culminated Tuesday in Keenan’s vaccination by Parsons, a nurse originally from the Philippines who has worked for the NHS for 24 years.

“I’m just glad to be able to play a part on this historic day,” she said. “The last few months have been tough for all of us working in the NHS, but now it feels like there is a light at the end of the tunnel.”