AstraZeneca and Oxford University's COVID-19 vaccine is more effective when its second dose is given three months after the first, instead of six weeks, a peer-reviewed study published in The Lancet medical journal showed on Friday.

The study confirmed the Anglo-Swedish drugmaker's findings from earlier this month that showed the vaccine had 76 percent efficacy against symptomatic coronavirus infection for three months after the first dose.

Efficacy was found to be at 81 percent with the longer interval of 12 weeks between the first and second dose, compared with 55 percent efficacy up to the six-week gap, according to the Lancet study, which backs British and WHO recommendations for longer intervals.

Faced with a resurgence in infections and new, highly transmissible variants of the virus, many countries are hoping to broaden immunization by giving some protection to as many people as possible with a first dose, while delaying subsequent shots.