The safety and efficacy of the Oxford COVID-19 vaccine has been confirmed in a published study but regulators will have to grapple with a dilemma over the optimum dosage.

The 62% efficacy for the planned vaccine dose, foreshadowed in the release of interim data two weeks ago, puts manufacturer AstraZeneca “in a difficult situation”, says pandemic expert Professor Raina MacIntyre from the Kirby Institute, UNSW Sydney.

Data published in The Lancet on Tuesday show that among 1300 patients who accidentally received a half-dose followed by the full-dose, the efficacy was 90%, making for a ‘combined efficacy’ of 70.4%, according to the authors.

But they admitted more research was needed to confirm these results “which will be done in future analyses of the data accruing in these ongoing trials”.