An earlier English study, published in May, found that the Pfizer-BioNTech vaccine was 88% effective at preventing symptomatic disease from the delta variant. Against the alpha variant, once the dominant strain in the U.K., the vaccine was 93% effective at preventing symptomatic disease.
Meanwhile, the research found that two doses of the Oxford-AstraZeneca vaccine were 60% effective at preventing symptomatic disease from the delta variant, compared to a 66% efficacy rate against the alpha variant.
Covid-19 vaccines are still "stunningly effective" despite fears that immunity may dwindle over time, experts have said.
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