The trial will examine the responses to an initial dose of Pfizer vaccine followed by a booster of AstraZeneca’s, as well as vice versa, with intervals of four and 12 weeks.

While thousands of individual changes have arisen as the virus mutates on replication and evolves into new variants, only a tiny minority are likely to be important or change the virus in an appreciable way, according to the British Medical Journal.

Among coronavirus variants currently most concerning for scientists and public health experts are the so-called British, South African and Brazilian variants, which appear to spread more swiftly than others.

British Vaccine Deployment Minister Nadhim Zahawi said current COVID-19 vaccines would probably still protect people against infection with the new variants, but this would need to be closely monitored.