A primary analysis of late-stage trial data has backed the safety and efficacy of AstraZeneca/Oxford University's COVID-19 vaccine, with 100% protection against severe disease, hospitalisation and death.

According to the analysis – of data from Phase III clinical trials in the UK, Brazil and South Africa and published as a preprint in The Lancet – there were no severe cases and or hospitalisations observed more than 22 days after the first dose of the vaccine was administered.

AstraZeneca said that results showed vaccine efficacy of 76% after a first dose, with protection maintained to the second dose. With an inter-dose interval of 12 weeks or more, vaccine efficacy increased to 82%, which is particularly good news given the UK's vaccination strategy.

Also crucial, the analysis showed the potential for the vaccine to reduce asymptomatic transmission of the virus, based on weekly swabs obtained from volunteers in the UK trial, with PCR positive readings cut by 67% after a single dose, and 50% after the two dose regimen, “supporting a substantial impact on transmission of the virus”.

“This primary analysis reconfirms that our vaccine prevents severe disease and keeps people out of hospital,” said Sir Mene Pangalos, executive VP BioPharmaceuticals R&D, commenting on the data. “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.”

“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,” added Professor Andrew Pollard, chief investigator of the Oxford Vaccine Trial, and co-author of the paper.

“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.”

The data will continue to be analysed and shared with regulators around the world to support ongoing rolling reviews for emergency supply or conditional approval, and AZ said it is also Emergency Use Listing from the World Health Organization for an accelerated pathway to vaccine availability in low-income countries.