The University of Oxford-AstraZeneca vaccine has one clear advantage over its early rivals in that it can be stored at higher temperatures when it travels to vaccination centres.

Refrigerated vans can transport the vaccine at 2°C to 8°C as long as it is protected from light.

Figures from the team behind the medicine also show the dose can be delivered four to eight weeks later, meaning the first round of injections can be carried out across a much wider population sample.

What matters is getting the vaccine into people's arms, according to Andrew Pollard, a scientist on the Oxford Vaccine Group.

The British regulator, the Joint Committee on Vaccination and Immunisation, said the priority should be to give as many people in at-risk groups their first dose, rather than providing the required two doses in as short a time as possible.

The UK has 100 million doses of the Oxford vaccine available. Its cost is no more than a cup of coffee at less than $5. Meanwhile, it is reported that the Moderna vaccine is being priced at $38 a dose and Pfizer-BioNTech at $20.

These rely on breakthrough genetic sequencing technology known as mRNA wrapped inside fat droplets. The AstraZeneca shot is a "viral vector vaccine", where a specially engineered virus that normally causes chimpanzees to get the common cold delivers genetic instructions to human cells to make the spike protein jutting out from the new coronavirus's surface.

The Moderna vaccine requires a 100-microgram dose versus Pfizer-BioNTech's 30mg.

The doses must be stored at minus 30°C and minus 70°C respectively.

Another important benchmark is that efficacy of the inoculation. Single-dose efficacy was 52.7 per cent, according to guidance to health workers. A UK medical adviser said that one AstraZeneca dose should be 70 per cent effective after three weeks.

The UK regulator recommends a booster shot four to 12 weeks after the first dose, because up to 80 per cent efficacy was reached with a three-month interval between shots, an official involved in the approval decision by the Medicines and Healthcare products Regulatory Agency (MHRA) said.

The pandemic has killed an estimated 1.7 million people around the world, devastated the global economy and upended normal life for billions since it began in Wuhan, China, a year ago.

Britain and South Africa in particular are grappling with new variants of the coronavirus, which the government and scientists say are more contagious. Many countries responded by banning passenger flights and blocking trade.

AstraZeneca and other developers said they are studying the effect of the new variant but expect that their vaccinations will be effective against it.

AstraZeneca's chief executive Pascal Soriot said the company would work with health authorities to ensure the vaccine worked against all strains.

"Our belief at this point is that this vaccine should be effective against the variant," he said on Wednesday.

Danny Altmann, professor of immunology at Imperial College London, said the vaccine release could be a "game-changer" at a time when the virus was outrunning even the more draconian efforts to contain transmission.

"To get out of this debacle there is no alternative to having a significant majority of the population carrying a high level of neutralising antibodies. With today's announcement, that comes within our grasp," he said.

"I await the modelling, but I suspect this will speed things by several months. An immune population by the spring starts to look feasible."