The Oxford-AstraZeneca's COVID-19 vaccine showed 76 percent efficacy against symptomatic infection for three months after a single dose, with protection maintained to the second dose, the pharmaceutical company said on 3 February.

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The primary analysis of the Phase 3 clinical trials, published as a preprint in The Lancet, also showed that with an inter-dose interval of 12 weeks or more, vaccine efficacy increased to 82 percent. "These new data provide an important verification of the interim data that has helped regulators such as the MHRA in the UK and elsewhere around the world to grant the vaccine emergency use authorisation," co-author Andrew Pollard, Chief Investigator of the Oxford Vaccine Trial, said in a statement.

"It also helps to support the policy recommendation made by the Joint Committee on Vaccination and Immunisation for a 12-week prime-boost interval, as they look for the optimal approach to roll out, and reassures us that people are protected 22 days after a single dose of the vaccine," Pollard added.

The analysis also showed the potential for the vaccine to reduce asymptomatic transmission of the virus, based on weekly swabs obtained from volunteers in the UK trial. The data showed that PCR positive readings were reduced by 67 percent after a single dose, and 50 percent after the two dose regimen, supporting a substantial impact on transmission of the virus. The primary analysis for efficacy was based on 17,177 participants accruing 332 symptomatic cases from the Phase 3 in UK, Brazil and South Africa trials led by Oxford University and AstraZeneca, a further 201 cases than previously reported.

The analysis also showed that the vaccine is safe and effective at preventing COVID-19, with no severe cases and no hospitalisation, more than 22 days after the first dose. AstraZeneca continues to engage with governments, international organisations and collaborators around the world to ensure broad and equitable access to the vaccine at no profit for the duration of the pandemic, the company said.