The world faces around 4,000 variants of the virus that causes COVID-19, prompting a race to improve vaccines, Britain said, as researchers began to explore mixing doses of the Pfizer and AstraZeneca shots https://reut.rs/3pNKqbx  1/5

Thousands of variants have been documented as the virus mutates, including the so-called British, South African and Brazilian variants which appear to spread more swiftly than others 2/5

While thousands of variants have arisen as the virus mutates on replication, only a very small minority are likely to be important and to change the virus in an appreciable way, according to the British Medical Journal 3/5

The so called British variant has mutations including a change in the spike protein that viruses use to bind to the human ACE2 receptor - meaning that it is probably easier to catch 4/5

Britain also launched a trial to assess the immune responses generated if doses of the vaccines from Pfizer and AstraZeneca are combined in a two-shot schedule. Read more https://reut.rs/3rjp85U  by @GuyReuters @asmo17 5/5