EG.5 and EG.5.1 are descendants of Omicron, which was first detected in South Africa in late-2021 before becoming widespread in the UK.
This week the World Health Organisation (WHO) designated EG.5 as a 'variant of interest' after it was reported in 51 countries.
Here Sky News looks at it in more detail.
When was it discovered?
EG.5 was first detected on 17 February but was given 'variant under monitoring' status by WHO on 19 July following a spike in cases, particularly in Asia. As of 7 August it was a 'variant of interest'.
According to the latest UK Health Security Agency (UKHSA) data, it is now the second most prevalent variant making up 11.8% of UK cases as of 27 July. As of 4 August, it represented one in seven UK infections.
The majority of cases are still the Arcturus strain, another Omicron sub-variant that emerged earlier in the year.
On a global scale, WHO claims EG.5 makes up 17.4% of infections as of 23 July, which it says is a "notable rise" on the last time it collected data on 25 June.
What are the symptoms?
According to the ZOE health app, the symptoms of EG.5 and EG.5.1, are similar to other Omicron sub-variants.
These include:
Runny or blocked nose
Headache
Fatigue
Sore throat
Sneezing
How worried should we be?
WHO has said that on the evidence available the "public health risk posed by EG.5 is low at global level" and similar to the other Omicron sub-variants we've seen in the past two years.
They haven't found an increase in disease severity compared to ones we've seen previously either.
But it does have a growth advantage and immune escape properties, which means it can evade natural or vaccine-based immunity.
It predicts that: "Due to its growth advantage and immune escape properties, EG.5 may cause a rise in case incidence and become dominant in some countries or even globally."
There have been increases in COVID hospitalisations in some Asian countries where EG.5 is circulating but there is no evidence of a link between the sub-variant and any spike in hospital admissions.
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