This has led AstraZeneca to announce a new global trial using the lower-dose regimen, although this is not expected to affect the timeline for regulatory approval and rollout of the vaccine in the UK and Europe.

Speaking on BBC Radio 4’s Today programme, Prof David Salisbury, a former director of immunisation at the Department of Health, said the further trials were important.

“If this vaccine came through at truly 90% and it is a cheaper vaccine and it requires much less rigorous cold chain than the RNA vaccines [from Moderna and Pfizer/BioNTech], then that would be a great result,” he said.

“But if it comes through at 62% and the other vaccines that are coming through so far are coming through at 90% then I think you have to think very carefully, what do we do with 100m doses of a product that isn’t protecting as well as the alternatives.”