Stealth Omicron in Leeds: 20 per cent of analysed Covid cases new coronavirus strain BA.2

The Wellcome Sanger Institute analysed 683 positive tests and identified that 136 of them were the Stealth Omicron variant.

The Omicron sub-variant, officially called BA.2, has been in the UK for some time - the first example was found on December 6, 2021.

It now accounts for more than half of cases in some parts of England.

But with case numbers growing in all regions of the UK, it is now on track to become the dominant strain.

Stealth Omicron got its nickname because it is more difficult to differentiate from Delta than the original Omicron variant, BA.1.

It also appears to be more contagious.

A spokesperson for the UK Health Security Agency (UKHSA) said its “apparent growth advantage is currently substantial”, when compared with Omicron.

Early studies show it takes around three days for Stealth Omicron to spread from an infected person to their contacts, half a day shorter than with Omicron.

Experts believe this may account for its faster spread.

There is no detected change in the effectiveness of vaccines against symptomatic infection.

And there is not yet enough data to show whether BA.2 causes more severe disease than the original Omicron variant.

The World Health Organisation said the BA.2 variant is now dominant in 10 countries worldwide, including China, India and Denmark.

It said: “Overall, there is no difference in severity when looking at countries where BA.2 is dominant and those where BA.1 is dominant.”

The Wellcome Sanger Institute analysed 38,000 positive Covid-19 tests taken in the week to February 12 to determine which variant they were.

Analysis of this data shows that one in four samples (25%) are now Stealth Omicron across England.

There are two local authority areas where BA.2 is already the dominant strain - Woking and Northampton.

Areas with fewer than 10 samples have been omitted.

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