Two doses of the Oxford/AstraZeneca Covid-19 vaccine is around 85% to 90% effective against symptomatic disease, Public Health England (PHE) said on Thursday, citing an analysis of real-world data from the rollout of the shot.
Britain has suffered one of the worst death tolls globally from the pandemic, but has also had one of the fastest rollouts of Covid-19 vaccines, generating a lot of data about the use of the shots in real world settings.
In a weekly surveillance report, Public Health England said that the estimated effectiveness of the AstraZeneca vaccine, invented at the University of Oxford, was 89% compared to unvaccinated people.
That compares to 90% estimated effectiveness against symptomatic disease for the Pfizer/BioNTech vaccine.
"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% protection," vaccines minister Nadhim Zahawi said.
PHE said there was a "small reduction in vaccine effectiveness" from 10 weeks after the first dose. Britain 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, Britain cut the gap between doses down to 8 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.
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 also estimated that the Covid-19 vaccine programme overall had prevented the deaths of 13,000 over-60s up to May 9, and stopped 39,100 of those over 65 from needing hospital treatment from Covid-19.