Two doses of Pfizer or AstraZeneca’s Covid-19 vaccine are nearly as effective against the highly transmissible Delta coronavirus variant as they are against the previously dominant Alpha variant, a study published on July 21 showed.

Although there have been discussions about using different Covid-19 vaccines in combination, World Health Organization (WHO) chief scientist Soumya Swaminathan warned against it, calling it a “dangerous trend.”

Britain said on July 7 the country would provide genomic sequencing support to Brazil, Ethiopia, Kenya, Nigeria and Pakistan to help identify, assess and track new variants of the novel coronavirus.

The Pfizer-BioNTech vaccine is highly effective against the Delta variant of Covid-19, a Pfizer official in Israel said on June 24.

Covid-19 vaccines made by AstraZeneca and the Pfizer-BioNTech alliance remain broadly effective against Delta and Kappa variants of the Covid-19 causing virus that were first identified in India, according to a scientific study, underpinning a continued push to deliver the shots.

A double dose of Covid-19 vaccines is almost as effective against the fast-spreading variant of the coronavirus first identified in India as it is against Britain’s dominant strain, English health officials said on May 22.

Two doses of the Oxford/AstraZeneca Covid-19 vaccine are around 85 percent to 90 percent effective against symptomatic disease, Public Health England (PHE) said on May 20, citing an analysis of real-world data from the rollout of the shot.

Covid-19 vaccines deployed in England can cut transmission of the coronavirus in households by up to a half, data from Public Health England (PHE) showed on April 28, in addition to the protection the shots offer against symptomatic infection.

Public Health England (PHE) published real-world analyses of people in the U.K. who had received the first shot of the Pfizer-BioNTech Covid-19 vaccine, with the data – which were published in The Lancet – showing that there was a decrease of about 70 percent in infections among healthcare workers after the first shot.