The Oxford vaccine may stop asymptomatic infection in a crucial sign that it could provide herd immunity.
The team behind the drug has become the first to provide preliminary evidence that theirs did more than just stop illness.
But in a further dilemma for regulators, the strongest effect seems to come from the “half dose” regimen that was discovered by chance.
Scientists said the findings, published in The Lancet yesterday, could further complicate the decision about which strategy to use, as the group given this apparently more effective dosing regimen was also smaller and did not include older adults.
According to the results, those receiving first a half dose and then a full dose had an estimated 90 per cent protection against symptomatic illness