The variant has gone from accounting for about 10 per cent of all Covid cases in May to almost 40 per cent three weeks later in mid-June.
Stratus—a descendent of the already super virulent Omicron—is what is known as a Frankenstein or ‘recombinant’ strain.
This means it emerged when a person was infected with two Covid strains at once which then became a new hybrid variant.
Professor Lawrence Young, a virologist at Warwick University, told MailOnline both two strains of Stratus—the original XFG and spin off called XFG.3— are ‘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, more people will be susceptible to infection with XFG and XFG.3.
‘This could lead to a new wave of infection but it’s difficult to predict the extent of this wave.’
However, he added that there is currently no evidence Stratus causes more severe illness and getting a Covid vaccine was ‘very likely’ to offer protection from severe illness and hospitalisation.
Stratus’ rise comes just a week after the World Health Organisation (WHO) declared the strain a ‘variant under monitoring’.
This designation means health authorities across the globe have been asked to help track the variant due its rising spread in different countries and the potential public health implications.
Whilst assessing the overall risk of Stratus as ‘low’ the WHO said evidence pointed to the variant having significant growth advantage compared to other strains with it now accounting for 22 per cent of cases recorded globally.
Nimbus—another new Covid variant also tipped to drive a wave of new infections—has also soared in recent weeks.
That strain has gone from just 2 per cent of cases in April to 17 per cent in June, according to UKHSA data.