The latest data came as coronavirus cases surge across Europe, making the continent the epicentre of the pandemic again.

Meanwhile, a new variant of the coronavirus with a "constellation" of mutations has been identified in Botswana.

Designated as B.1.1.529, scientists are still unclear whether existing antibodies would react well to the variant, which has 32 spike protein mutations.

Tom Peacock, a virologist at Imperial College London, branded the mutations "really awful" on Twitter.

"Given the large number of mutations it has accumulated apparently in a single burst, it likely evolved during a chronic infection of an immunocompromised person, possibly in an untreated HIV/AIDS patient," said Francois Balloux, professor of computational systems biology and director of Genetics Institute at University College London.

"For the time being, it should be closely monitored and analysed, but there is no reason to get overly concerned, unless it starts going up in frequency in the near future," Balloux said.