Other countries are not far behind. The US and the European Union also are vetting the Pfizer shot along with the vaccine by competitor Moderna.

Pfizer said it would immediately begin shipping limited supplies to the UK – and has been gearing up for even wider distribution if given a similar nod by the US Food and Drug Administration, a decision expected as early as next week.

The UK will start vaccinating people early next week after it gets 800,000 doses from Pfizer’s manufacturing centre in Belgium. The speed of the rollout depends on how fast Pfizer can manufacture and deliver the vaccine, the UK said.

But doses everywhere are scarce, and initial supplies will be rationed until more is manufactured in the first several months of next year.

Danny Altmann, professor of immunology at Imperial College London, said: “Exciting news keeps coming, but this really is momentous. Nobody knew how the battle to find effective vaccines would pan out. Now, less than 11 months from the first characterisation of the virus sequence, we have the first emergency approval for use of a really effective vaccine.

“Truly heroic. I don’t think we should get too hung up on ‘the race’ and this as the first approval. Over the next several weeks we’ll likely see a number of licenses granted – and we do need them all to get speedily out of this mess.”

Fifty hospitals are set up across England and waiting to accept the vaccine, large vaccination centres are being set up now, and in time local health centres known as general practitioners (GPs) and pharmacists will provide the jab in the community if they have those capabilities

UK regulators also are considering another shot made by AstraZeneca and Oxford University.

But PM Johnson has warned “we must first navigate a hard winter” of restrictions to try to curb the virus until there is enough vaccine to go around.

Every country has different rules for determining when an experimental vaccine is safe and effective enough to use.

Intense political pressure to be the first to roll out a rigorously scientifically tested shot coloured the race in the US and UK, even as researchers pledged to cut no corners.

In contrast, China and Russia have offered different vaccinations to their citizens ahead of late-stage testing.

Tested in tens of thousands
The shots made by Pfizer and BioNTech were tested in tens of thousands of people.

While that study is not complete, early results suggest the vaccine is 95 percent effective at preventing mild to severe COVID-19 disease.

The companies told regulators that of the first 170 infections detected in study volunteers, only eight were among people who had received the actual vaccine and the rest had gotten a dummy shot.

“We know that Pfizer can have only 1.3 billion doses by the end of next year. That is definitely not going to vaccinate the world, but we are going to take this first crucial step which is exciting,” Oksana Pyzik, a teaching fellow at the UCL School of Pharmacy, told Al Jazeera.

“The timeline has been fast, but also we need to think about this unique context that we are in – we have over 200 companies that have been focusing on developing a vaccine, they have unlimited resources and all of the world’s talents have been focused on this problem.”

The companies also reported no serious side effects, although vaccine recipients may experience temporary pain and flu-like reactions immediately after injections.

But experts caution that a vaccine cleared for emergency use is still experimental and final testing must be completed. Still to be determined is whether the Pfizer-BioNTech shots protect against people spreading the coronavirus without showing symptoms.

The vaccine also has been tested in only a small number of children, none younger than 12, and there is no information on its effects on pregnant women.

Al Jazeera Media Network