Two doses of the Oxford/AstraZeneca Covid-19vaccine are around 85-90 per cent effective against symptomatic disease, Public Health England said on Thursday, citing analysis of real-world data from the rollout of the shot.
The UK has suffered one of the worst death tolls globally from the pandemic, but has also had one of the fastest vaccine rollouts - generating a lot of data about the use of the shots in real world settings.
In a weekly surveillance report, PHE said the estimated effectiveness of the AstraZeneca vaccine, invented at the University of Oxford, was 89 per cent compared to unvaccinated people.
"This new data highlights the incredible impact that both doses of the vaccine can have, with a second dose of the Oxford/AstraZeneca vaccine providing up to 90 per cent protection," vaccines minister Nadhim Zahawi said.
PHE said the analysis was the first of its kind on the effectiveness of two doses of AstraZeneca in a real-world setting but was not yet published in a journal, adding more data would boost its confidence in the finding.
Britain has been rolling out the shots manufactured by Pfizer and AstraZeneca since December and January respectively, and in April also started rolling out Moderna's vaccine.
PHE said there was a "small reduction in vaccine effectiveness" from 10 weeks after the first dose of the Pfizer shot before the second shot is given.
The UK extended the gap between doses to 12 weeks, though Pfizer warned there was a lack of evidence of its efficacy outside the three-week gap used in trials.
Last week, the UK cut the gap between doses down to eight weeks for the over 50s, aiming to give maximum protection to more vulnerable people in light of concern about the B.1.617.2 variant first found in India.