A highly contagious Covid strain has emerged and is already behind one in 25 cases in the UK, data suggests
What is XBB.1.5?
XBB.1.5 is a new Covid variant that is sparking concern across the world.
The strain is a mutated version of Omicron XBB, which was first detected in India in August.
XBB, which is a merger of variants BJ.1 and BA.2.75, caused cases to quadruple in just one month in some nations.
XBB.1.5 has gained additional mutations, including F486P, which help it to bypass Covid-fighting antibodies that were generated in response to vaccination or previous infection.
Another change — S486P — is thought to improve its ability to bind to cells.
Where has it been spotted?
Concern about XBB.1.5 is largely based on how it is currently sweeping the US — but it has also already been spotted in Britain and other countries around the globe.
Data from the US Centers for Disease Control and Prevention (CDC) on Friday showed that the strain is behind 41 per cent of cases. The figure is up from 22 per cent one week earlier.
Figures from the Sanger Institute, one of the UK’s largest Covid surveillance centres, shows 4 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.
XBB.1.5 has also been spotted in countries including France, Germany, the Netherlands, Spain, Ireland, Australia, Singapore and India.
Is the variant concerning?
Experts are concerned XBB.1.5’s rapid rise in the US could be caused by mutations that help it to better infect people and dodge protection from vaccination and prior infections.
Professor Lawrence Young, a virologist at Warwick University, told MailOnline that the emergence of the strain is a ‘wake-up call’ and could exacerbate the NHS crisis in Britain.
Professor Paul Hunter, an epidemiologist at the University of East Anglia, told MailOnline that the majority of new variants ‘fizzle out in a few weeks’.
However, the sharp increase in XBB.1.5’s prevalence is ‘certainly very worrying’ and suggests ‘a pretty dramatic growth advantage and enough to drive a new wave of infections’, he said.
Why are some scientists not worried?
Dr Simon Clarke, a microbiologist based at the University of Reading, told MailOnline that while XBB.1.5’s ability to evade immunity has only been observed in the lab.
‘So it’s difficult to know how this will translate into real life,’ he noted.
While hospital admissions in the US are rising in many regions, ‘the presence of this variant doesn’t seem to be responsible for that’, Dr Clarke said.
Also, it doesn’t seem to be causing more serious disease than other circulating variants, which are the most important metrics to watch when tracking Covid, he said.
Dr Clarke added: ‘It will be interesting to see how the situation develops over the coming months as the usual annual wave of flu hospitalisations is usually highest in January and February.’
Professor Francois Balloux, an infectious disease expert based at University College London, told MailOnline that XBB.1.5 cases ‘will likely go up in frequency globally’ in the near future.
He added: ‘As such, it would contribute to push case numbers higher over the coming weeks. That said, it is far from clear XBB.1.5 will cause a massive wave on its own.’