Primary analysis of phase III trials also showed that the vaccine efficacy is stronger when the period between the two doses is lengthened to 12 weeks.
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AstraZeneca said on Wednesday that a single dose of its vaccine can protect against the virus for over three months and reduce its spread by two thirds.
Primary analysis of Phase III clinical trials from the UK, Brazil and South Africa showed that the vaccine was 76 per cent effective at preventing COVID-19 — with no severe cases or hospitalisations — after a single dose. The rate increased to 82 per cent after a second jab administered 12 weeks or more after the first.
Additionally, a single dose of the jab led to a 67 per cent reduction on positive PCR tests which suggests the vaccine has "a substantial impact on transmission of the virus," AstraZeneca said.
The primary analysis was based on results from more than 17,100 participants.
Sir Mene Pangalos, Executive Vice President BioPharmaceuticals R&D, said in a statement that "this primary analysis reconfirms our vaccine prevents severe disease and keeps people out of hospital."
"In addition, extending the dosing interval not only boosts the vaccine's efficacy, but also enables more people to be vaccinated upfront. Together with the new findings on reduced transmission, we believe this vaccine will have a real impact on the pandemic," he added.
Britain's Health Minister, Matt Hancock, described the results as "absolutely superb".
The government had in December heeded the advice of the Joint Committee on Vaccination and Immunisation (JCVI) and extended the inter-dose interval to up to 12 weeks — from an initial recommendation of 28 days — as preliminary data suggested a lengthier period offered greater protection. The decision also enabled the authorities to offer a first jab to more people.
The latest figures from AstraZeneca, which show efficacy rising from 56 per cent when the second dose is administered less than six weeks after the first to more than 82 per cent when given 12 weeks later, validate that position.
The data from the British-Swedish pharmaceutical group comes a day after France, Poland and Sweden joined Germany and Italy in recommending that the AstraZeneca jab not be used for the elderly, citing insufficient data over efficacy for older age groups.