LONDON • AstraZeneca and Oxford University have more work to do to confirm if their Covid-19 vaccine can be 90 per cent effective, a peer-reviewed paper in The Lancet showed on Tuesday, potentially slowing its roll-out in the fight against the pandemic.

Once seen as the front runner in the development of a vaccine against the coronavirus crisis, the British team was overtaken by US drugmaker Pfizer, whose shots - with a success rate of around 95 per cent - were administered to British pensioners on Tuesday in a world-first hailed as V-Day.

Detailed results from the AstraZeneca/Oxford vaccine trials have been eagerly awaited.

But the Lancet publication gave few extra clues as to why efficacy was 62 per cent for trial participants given two full doses, but 90 per cent for a smaller sub-group given a half, then a full dose.

"(This) will require further research as more data becomes available," the researchers said.

Virologist John Moore of Weill Cornell Medical College in New York said the team's Lancet paper was "a hotchpotch of factoids and is hard to digest".

Asked if the half-, then full-dose regimen, had been a mistake, Professor Andrew Pollard, director of the Oxford Vaccine Group and chief investigator into the trials, said it had been "unplanned".

Less than 6 per cent of British trial participants were given the lower dose regimen and none of them was over 55, so more studies are needed to investigate the vaccine's efficacy in older people.

"The important thing today is that we have put all of our data into a publication in the Lancet which has been peer reviewed and been through that scientific scrutiny," Prof Pollard said.

REUTERS