A new sub-variant of Omicron emerging in the UK is being watched closely by health officials after case numbers are estimated to have doubled in a fortnight.

The World Health Organisation has warned that Omicron XE is likely to be more transmissible than previous variants of Covid-19 so here's what we know so far:

What is Omicron XE?

Omicron XE is known as a recombinant variant. This is because it is combining the genetic material of the two previous Omicron variants circulating in large numbers in the UK. These are known as BA.1 and BA.2 and are the UK's most dominant variants of the virus.

This type of sub-variant is created when those original variants manage to infect the same cell in the same patient at the same time and combine their genetic material. That sub-variant consequently created - called XE in this case - is then able to be passed on to others.

How quickly is Omicron XE spreading?

Omicron XE was first identified in the UK back in January and since then has been found in most English regions.

Towards the end of March the UK Health Security Agency said around 600 cases of Omicron XE had been identified - albeit the numbers of people now testing for coronavirus or sending official swabs for assessment is dwindling all of the time as a result of fewer restrictions being in place.

But latest figures suggest this is rising swiftly with 1,179 cases more recently identified around a fortnight later with the majority of XE cases thought to currently be across the south east and east of the country.

With fewer people testing and free tests no longer available for the majority of people then official numbers are likely to be much higher. The ONS estimates that around four million people in the UK could currently have coronavirus.

A very small number of cases of XE have also been identified in the Far East and Australia - possibly as a result of international travel.

What is the concern?
The World Health Organisation says it believes Omicron XE is very contagious. Original strains of the Omicron variant were already highly infectious but this recombinant variant is thought to pass from person to person very easily.

The UK Health Security Agency estimates, according to the most recent data it has available, that XE has a growth rate of 9.8 per cent above its parent variant BA.2.

Albeit with only small numbers of cases so far available for assessment, health officials were quick to stress this is only an estimation and exactly how the sub-variant spreads continues to be under investigation and it is not possible to draw any firm conclusions just yet.

But all new variants are closely monitored worldwide in order to track how effective current vaccines are against them or whether symptoms and illness is likely to be more severe than previous strains.

Does XE cause different symptoms?

Those thought to have been infected with the Omicron variant, and who are fully vaccinated, mostly report from suffering from cold and flu like symptoms that can differ significantly in their severity.

Fevers, sore throats, runny noses, congestion and fatigue are among the most common symptoms associated with Omicron and while medics continue to analyse available data from XE, it is felt the symptoms are likely to be similar.

What about vaccines?

Despite fewer coronavirus restrictions in place now in England, the government has stressed health officials will continue to closely monitor all new variants to ensure the country has adequate protections in place and any new threat can be identified and tackled straight away. This could be through anything from additional restrictions to new vaccines.

So far there is every indication that XE, while it may drive case numbers and higher infection rates, it doesn't seem to pose any more danger than either Omicron BA.1 or even Omicron BA.2 - which is thought to be weaker than the original.

And while we know that vaccines and booster jabs don't necessarily prevent you from catching Covid-19 health officials say they remain our best line of defence and ensure in the majority of cases that people become less sick and recover more quickly providing they've been fully vaccinated.

However in an article published last week by the World Economic Forum, discussing the new XE sub-variant, Queen's University Belfast virology research fellow Grace Roberts raised the prospect that in time vaccines that were first created to tackle the initial Wuhan strains of coronavirus may have to be altered to accommodate the growing numbers of new variants, including XE, the world is now seeing.

She wrote: "The need for updated vaccines is becoming ever-pressing since all current vaccines are based on the original Wuhan strain. Data has shown that the more changes in the spike protein subsequent variants have acquired, the less effective our current vaccines are at preventing infection.

"That said, vaccines are still very effective at preventing severe disease or death from COVID."