January 28, 2023

A highly contagious strain of Covid has emerged and is already behind one in 25 cases in the UK, surveillance data suggests.

The strain – dubbed XBB.1.5 – has raised alarm in the US due to its rapid spread and a recent rise in hospitalizations. It is behind four in ten cases in the country, up from two in ten just a week earlier.

The variant, a subvariant of Omicron, has mutations that help it better infect humans and evade protection from vaccination and previous infection.

Sequence data suggests it was already behind four per cent of UK cases the week before Christmas.

However, experts warn that there is no indication that the strain causes more serious disease than previous strains.

Highly contagious strain of Covid has emerged, already behind one in 25 UK cases, surveillance data suggests

Figures from the Sanger Institute, one of the UK's largest Covid surveillance centres, show that four per cent of cases in the week to December 17 were caused by XBB.1.5

Figures from the Sanger Institute, one of the UK’s largest Covid surveillance centres, show that four per cent of cases in the week to December 17 were caused by XBB.1.5

On December 17, XBB.1.5 was first listed on the institute's virus dashboard, which is updated weekly

On December 17, XBB.1.5 was first listed on the institute’s virus dashboard, which is updated weekly

Data from the U.S. Centers for Disease Control and Prevention (CDC) on Friday showed the strain is the cause of 41 percent of cases.

Dr. Barbara Mahon, director of the CDC’s Division of Coronavirus and Other Respiratory Viruses, said CBS news: ‘We predict that it will become the dominant variety in the northeast of the country and that it will increase in all regions of the country.’

She said: “There is no suggestion at this time that XBB.1.5 is more serious.”

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Covid hospitalizations have risen in the US and levels “do not appear to be increasing in the areas with more XBB.1.5,” Dr Mahon added.

Figures from the Sanger Institute, one of the UK’s largest Covid surveillance centres, show that four per cent of cases in the week to December 17 were caused by XBB.1.5.

It is the first time the strain has been listed on the institute’s virus dashboard, which is updated weekly.

The strain is a mutated version of Omicron XBB, first discovered in India in August.

XBB, a merger of variants BJ.1 and BA.2.75, caused the number of cases to quadruple in just one month in some countries.