The coronavirus vaccine developed by pharmaceutical company AstraZeneca and Oxford University is more effective when its second dose is given around three months after the first, instead of six weeks later, a peer-reviewed study published in medical journal The Lancet showed on Friday.

The efficacy of the vaccine was found to be 81.3% with a longer interval of 12 weeks between the first and second dose, compared to 55.1% efficacy in case of a six-week gap, according to the Lancet study. According to the researchers, including those from the Oxford University, the extended dosage regimen will be beneficial while vaccine supplies are initially limited, and may allow countries to immunise a larger proportion of the population more rapidly, PTI reported.

“Vaccine supply is likely to be limited, at least in the short term, and so policy-makers must decide how best to deliver doses to achieve the greatest public health benefit,” said study lead author Professor Andrew Pollard from the University of Oxford.

The study also confirmed AstraZeneca’s findings from earlier this month that showed that the vaccine had 76% efficacy against symptomatic coronavirus infection for up to three months after the first dose. However, the scientists said it is not yet clear how long protection with a single dose of the vaccine might last, since the trial results are limited to the three months. So, a second dose was still recommended, they said.

From the study, the researchers sought to understand the effect of different intervals on protection after the second dose, and the risk of infection between jabs – either due to lower efficacy of a single dose, or rapid waning of efficacy while waiting for the second dose. It study collected data of 17,178 adult participants from across the United Kingdom, Brazil and South Africa.

Earlier this week, the World Health Organization approved the Oxford-AstraZeneca coronavirus vaccine for emergency use, paving way for its distribution in developing countries through the COVAX programme.