Research published in the NEJM suggests two doses of Pfizer/BioNTech or AstraZeneca's COVID-19 vaccines are nearly as effective against the highly transmissible Delta variant as they are against the previously dominant Alpha variant, as reported in Fidelity.

The study confirms findings given by Public Health England in May, based on real-world data, about the efficacy of COVID-19 vaccines made by Pfizer/BioNTech and AstraZeneca.

The new study found that two doses of Pfizer/BioNTech's shot was 88% effective at preventing symptomatic disease from the Delta variant, compared to 93.7% against the Alpha variant, broadly the same as previously reported.

Meanwhile, two shots of AstraZeneca's vaccine were 67% effective against the Delta variant, up from 60% originally reported, and 74.5% effective against the Alpha variant, compared to an original estimate of 66% effectiveness.

However, one dose of Pfizer/BioNTech's shot was 36% effective, and one dose of AstraZeneca's vaccine was around 30% effective.

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