Three weeks later, in mid-June, the variation accounted for about 40% of all Covid cases, up from roughly 10% in May.

A “recombinant” or Frankenstein strain, Stratus is a descendant of the already extremely virulent Omicron.

This indicates that it developed as a new hybrid variation when an individual contracted two Covid strains simultaneously.

Warwick University virologist Professor Lawrence Young told MailOnline that the original XFG strain and its spin-off, XFG.3, are both “rapidly spreading.”

“The increased competitiveness of XFG and XFG.3 is likely due to new spike mutations which make these variants more able to evade the immune response,” he said.

“Given that immunity to Covid is waning in the population due to a decline in uptake of the spring booster jab and the reduction of Covid infections in recent months