RIO DE JANEIRO, BRAZIL – Two doses of Pfizer and AstraZeneca’s Covid-19 vaccines are nearly as effective against the highly transmissible Delta variant of the coronavirus as against the previously dominant Alpha variant in several countries around the world, a study published Wednesday showed.
Officials say the vaccines are highly effective against the Delta variant, now the dominant strain in most of the world, although the study reiterated that one dose of the vaccines alone is not enough for high protection.
The study, published in the New England Journal of Medicine, confirms key findings provided by the British government in May on the effectiveness of Covid-19 vaccines made by Pfizer-BioNTech and Oxford-AstraZeneca, based on real-world data.
The study released on Wednesday pointed out that two doses of Pfizer’s vaccine resulted in 88% efficacy in preventing symptomatic disease of the Delta variant, compared to 93.7% against the Alpha variant, in line with what was previously reported.
Two doses of AstraZeneca’s vaccine resulted in 67% efficacy against the Delta variant, up from 60% originally reported, ante 74.5% against the Alpha variant, compared to an original estimate of 66% efficacy.
“Only modest differences in vaccine efficacy were observed with the Delta variant compared with the Alpha variant after receiving two doses of the vaccine,” researchers from the Department of Public Health England wrote in the study.
Data from Israel estimated lower efficacy of Pfizer’s vaccine against symptomatic illness caused by Delta, although protection against the severe disease remains high.
The study published Wednesday found that one dose of Pfizer’s injection was 36 percent effective, and one dose of AstraZeneca’s vaccine was about 30 percent effective.
“Our finding of reduced efficacy after the first dose supports efforts to maximize two-dose vaccine delivery among vulnerable groups in the context of Delta variant circulation,” the study authors said.