The Oxford AstraZeneca is more effective when the second dose is given three months after the first, instead of six weeks, a peer-reviewed study published in The Lancet medical journal.
The study found that the vaccine had 76% efficacy against symptomatic coronavirus infection for three months after the first dose.
Efficacy was found to be at 81% with an interval of 12 weeks between the first and second dose, compared to 55% with the six-week gap, which backs British and WHO recommendations for longer intervals.