There are fears a new Covid variant could be about to add to the immense strain the NHS is under this winter.

Accounting for more than 40% of cases in the US last month, scientists on this side of the Atlantic are now said to be watching carefully the emergence of a new variant of Omicron and here's what we know so far.

What is the new variant called?

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

Omicron is highly transmissible and was subsequently behind the sharp rise in cases and hospital admissions across the UK last winter. Different strains of Omicron have also over the last 12 months accounted for the majority of infections detected around the globe surpassing previous variants of coronavirus such as Alpha and Delta that were responsible for early waves in the pandemic.

How fast is it spreading?

The majority of 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% of cases are being attributed to XBB.1.5 - up 20% from a week ago - and still steadily rising say scientists at the US-based Centers for Disease Control and Prevention. In the north of the country the figure could be as high as 75% of all cases, where the variant is said to be spreading like 'wildfire'.

Hospitalisations are also now rising in New York, and with a known lag between rising infections and hospital admissions, there are fears that this new strain of Covid-19 is about to cause another wave of the virus particularly after a busy holiday season where people have travelled across the county to meet with friends and family.

According to some reports this week there are estimates in the US that XBB.1.5 is also spreading more than twice as fast as some of the most common variants currently found in the UK.

Why is it spreading so fast?

With testing having been scaled back in many countries over the last 12 months, perhaps the true number of cases connected to this new variant are hard to determine. Numbers in the UK are hard to pinpoint for the same reason, albeit current estimates suggest XBB.1.5 could be behind between 5% and 10% of cases according to the latest statistics from the third week of December.

However those studying XBB.1.5 believe 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 successfully attack the virus. Both mean that if people encounter a case of XBB.1.5 they are more likely to fall ill, get reinfected and show symptoms they may then pass onto others.

Is XBB.1.5 more dangerous?

There are no signs so far, says US doctor Barbara Mahon - director of CDC’s Coronavirus and Other Respiratory Viruses Division - that this new variant is causing a different or more severe illness.

In an interview this week with NBC News it was explained that while hospitals are seeing high rises in admissions they're 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 rising cases in America showed rapid spread was possible.

So why the concern?

While there is no current evidence to show that this new Covid-19 variant is more deadly, that doesn't mean it won't lead to 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 - with parents also being encouraged to keep children at home if they too appear under the weather.

With hospital A&E departments and GP surgeries facing huge demand for their services there have also been calls for a return to face masks with Professor Susan Hopkins, chief medical adviser at the UKHSA, already asking those who are unwell who need to leave the house to use a face covering to try and limit any spread of infection.