Britain on Wednesday, 30/12, became the first country to approve AstraZeneca and Oxford University's home-grown UK Covid-19 vaccine, adding an easy-to-manage shot to the arsenal of a nation desperate for pandemic relief.
Even so, scientists - and regulators in Europe, following the Brexit divorce - are sceptical, given confusion over trial results earlier that left experts questioning the robustness of the data.
HOW DOES THE ASTRAZENECA SHOT'S EFFICACY STACK UP TO OTHERS'?
The AstraZeneca/Oxford vaccine's efficacy in preventing symptomatic infections was 70.4%, according to interim data, after 30 of 5,807 people who got the two-dose vaccine developed Covid-19, compared with 101 of 5,829 people who got a placebo.
That compares with the 95% efficacy of the two-shot vaccine from Pfizer/BioNTech, the other vaccine approved in Britain.
While efficacy with any dose after one dose was pegged at 52.7%, the UK's Medicines and Healthcare products Regulatory Agency (MHRA) regulator also said an "exploratory analysis" of trial participants who got one full dose showed efficacy of 73% from 22 days after the first shot.
The UK regulator recommends a booster shot four to 12 weeks after the first dose, because up to 80% efficacy was reached with a three-month interval between shots, an official involved in the MHRA approval said.
"The first dose efficacy gives an indication of protection for a short period between the two doses, the second dose strengthens the immune response and is expected to provide a more durable immune response," the University of Oxford, AstraZeneca's partner, said.
Confusion over efficacy emerged after interim late-stage trial results announced in late November when AstraZeneca acknowledged that people in its clinical trial accidentally got different doses.
Those who received a half dose of the vaccine, followed by a full dose, were shown to have 90% protection, the company said initially, while two full doses offered only 62% protection.
Now, however, the MHRA said the half-dose regimen's results were not borne out in analysis.