Two doses of Pfizer AstraZeneca COVID-19 shots effective against delta variant study finds

Two doses of Pfizer-BioNTech or AstraZeneca-Oxford's COVID-19 vaccines are nearly as effective against the highly transmissible delta coronavirus variant as they are against the previously dominant alpha variant, a new study shows.

Officials say vaccines are highly effective against the delta variant, now the dominant variant worldwide â€" though the study reiterated that one shot of the vaccines is not enough for high protection.

The study, published in the New England Journal of Medicine on Wednesday, confirms headline findings given by Public Health England (PHE) in May about the efficacy of COVID-19 vaccines made by Pfizer-BioNTech and Oxford-AstraZeneca, based on real-world data.

The research team found that two doses of Pfizer's shot was 88 per cent effective at preventing symptomatic disease from the delta variant, compared to 93.7 per cent effective against the alpha variant, broadly the same as previously reported.

Two shots of the AstraZeneca vaccine were 67 per cent effective against the delta variant, up from 60 per cent originally reported, and 74.5 per cent effective against the alpha variant, compared to an original estimate of 66 per cent effectiveness.

"Only modest differences in vaccine effectiveness were noted with the delta variant as compared with the Alpha variant after the receipt of two vaccine doses," PHE researchers wrote in the study.

The research didn't look at the effectiveness of mixing brands for different doses, though ongoing U.K. research has shown the Pfizer-BioNTech and AstraZeneca-Oxford vaccines appear to generate a stronger immune response than having two rounds of the AstraZeneca shot.

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The World Health Organization says the trajectory for the COVID-19 delta variant in some countries is almost 'vertical' and warns that even partially vaccinated countries are at great risk because of its high transmissibility. (Willy Kurniawan/Reuters) 0:56 High protection against severe disease

Data from Israel has estimated lower effectiveness of Pfizer's shot against symptomatic disease, although protection against severe disease remains high.

PHE had previously said that a first dose of either vaccine was around 33 per cent effective against symptomatic disease from the delta variant.

The full study also found that one dose of Pfizer's shot was 36 per cent effective, and one dose of AstraZeneca's vaccine was around 30 per cent effective.

"Our finding of reduced effectiveness after the first dose would support efforts to maximize vaccine uptake with two doses among vulnerable groups in the context of circulation of the delta variant," the authors of the study said.

'All signs' point to delta taking over

Hamilton-based immunologist Matthew Miller, a McMaster University professor and member of school's Immunology Research Centre, called it a "strong study."

"I think it is really important, especially in the Canadian context right now, because all signs are pointing to delta rapidly taking over as the main variant circulating," he added.

Miller also noted the high level of effectiveness of two vaccines in the study, both of which have been used in Canada, is a good sign for the country moving forward.

"If we can continue our momentum and get second doses into people as we move into the end of July and August, we're really setting ourselves up for success in the fall and winter where, by necessity, people have to be indoors more," he said.

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