LONDON – Two doses of either Pfizer or AstraZeneca’s COVID-19 vaccine are almost as effective against the highly permeable delta coronavirus variant as they are against the previously dominant alpha version, a study published on Wednesday showed .

Officials say the vaccines are highly effective against the delta variant, which is now the dominant variant worldwide, although the study reiterated that a single shot of the vaccines is not enough for high protection.

the study, published in the New England Journal of Medicine, confirms headline findings made by Public Health England in May about the efficacy of COVID-19 vaccines created by Pfizer-BioNtech and Oxford-AstraZeneca based on real-world data.

Wednesday’s study found that two doses of Pfizer’s shot were 88% effective in preventing symptomatic disease from the delta version, compared with 93.7% against the alpha version, roughly the same as previously reported.

The two shots of the AstraZeneca vaccine were 67% effective against the delta version, higher than the 60% originally reported, and 74.5% effective against the alpha version, compared to the original estimate of 66% effectiveness.

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“Only a slight difference in vaccine effectiveness was noted with the delta version after receiving two vaccine doses compared with the alpha version,” the researchers from Public Health England wrote in the study.

Data from Israel predict a low effectiveness of Pfizer’s shot against symptomatic disease, although protection against serious disease remains high.

PHE previously stated that the first dose of any vaccine was about 33% effective against symptomatic disease from the delta variant.

The full study, published Wednesday, found that a single dose of Pfizer’s shot was 36% effective, and a single dose of AstraZeneca’s vaccine was about 30% effective.

“Our finding of reduced effectiveness after the first dose will support efforts to maximize the vaccine with two doses among vulnerable groups in terms of circulation of the delta variant,” the study authors said.

(Reporting by Alistair Smout; Editing by Barbara Lewis)