What we know about new Covid-19 variant XBB.1.5 spreading ‘like wildfire’ in US and now present in the UK

A new Covid-19 variant could be about to add to the great strain that the NHS is under this winter, it is feared.

It accounted for more than 40 per cent of cases in the US last month and scientists here - led by Cambridge-led COG-UK Consortium - are watching carefully for its emergence.

Here’s what we know about it.

What is the new variant called?

Currently known as XBB.1.5, the latest Covid-19 variant is a descendent of Omicron, the variant first detected in Botswana at the end of 2021.

Omicron, which is highly transmissible, was behind the sharp rise in cases and hospital admissions across the UK last winter.

Over the last year, various strains of Omicron have accounted for the majority of infections detected around the world, surpassing previous variants of Covid, such as Alpha and Delta, that were responsible for early waves in the pandemic.

How fast is it spreading?

Most XBB.1.5-related cases have so far been detected in America, where the number of infections at the end of December doubled in just a week.

Now, around 40 per cent of cases are being attributed to it – up 20 per cent from a week ago – and that is steadily rising say scientists at the US Centers for Disease Control and Prevention (CDC). In the north of the country, the figure could be as high as 75 per cent of all cases and the variant is said to be spreading like “wildfire”.

Hospitalisations are now rising in New York, reflecting the known lag between rising infections and hospital admissions. And there are concerns that this new strain of Covid-19 could lead to another wave of the virus, particularly after a busy holiday season during which people travelled across the county to meet with friends and family.

Some estimates in the US suggest XBB.1.5 is spreading more than twice as fast as some of the most common variants currently found in the UK.

The World Health Organization has called it the “most transmissible sub-variant that has been detected yet”.

Dr Maria Van Kerkhove, WHO’s technical lead for Covid, told a press conference: “We are concerned about its growth advantage in particular in some countries in Europe and in the US.”

Why is it spreading so fast?

Testing has been scaled back in many countries over the last 12 months, so the true number of cases caused by this new variant is harder to determine.

Numbers in the UK are hard to pinpoint for the same reason, but current estimates suggest XBB.1.5 may have caused five to 10 per cent in the third week of December.

Those studying XBB.1.5 say it has an unusual mutation that is helping it spread and making it harder for the antibodies people have gained from either vaccination or a previous Covid-19 vaccination to fend off the virus successfully. That could mean people encountering a case of XBB.1.5 are more likely to fall ill, get reinfected and show symptoms they may then pass onto others.

In particular, there are suggestions that the F486P mutation could help it to bypass Covid-fighting antibodies generated by vaccination or previous infection, while another change - S486P - may help it bind to human cells.

Is XBB.1.5 more dangerous?

US doctor Barbara Mahon – director of CDC’s Coronavirus and Other Respiratory Viruses Division – says there are now signs so far that this new variant is causing a different or more severe illness.

In an interview with NBC News it was explained that while hospitals are seeing high rises in admissions they are not disproportionate to the number of cases being recorded.

However, if the new variant spreads more quickly and easily it will infect more people and this increases the risk to the elderly, vulnerable and those with other underlying health conditions.

Tim Spector, professor of genetic epidemiology at King’s College London and founder of the Zoe app, tweeted that this new variant “could be the one to watch” this year after the rising cases in America.

Will we see more hospital admissions?

While there is no current evidence to show that this new Covid-19 variant is more deadly, we could still see a rise in hospital admissions if increasing numbers of people are infected.

And with the NHS already under immense pressure this month, health staff fear that another wave of Covid-19 would simply add to the significant pressure already on beds, resources, appointments and staff.

The UK Health Security Agency is appealing to those who are unwell to not visit the vulnerable or go into work because of already high rates of flu, Covid and Strep A infections that are circulating.

Parents are encouraged to keep children at home if they have a fever.

Hospital A&E departments and GP surgeries are facing huge demand for their services, which has prompted calls for a return to face masks.

Professor Susan Hopkins, chief medical adviser at the UKHSA, has already asked those who are unwell who need to leave the house to use a face covering to try and limit any spread of infection.