There have been no new cases of the Mu variant of interest in England within the two weeks leading up to 5 January 2022, the UK government has confirmed.


Despite this, Public Health England and the World Health Organization (WHO) are still closely monitoring the strain.

Some scientists have warned that the Mu strain, also known as B.1.621, could be a problem if it were to become the dominant variant. This is due to the Mu variant having the ability to spread more easily through cells in the human body, something that is also seen in the Delta variant.

Meanwhile, the Omicron variant has quickly overtaken Delta to become the dominant UK coronavirus strain. In the last two weeks, there have been 274,470 new Omicron cases reported.

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How many cases of the Mu variant have been detected in the UK?

According to UK government data, there have been a total of 59 cases of the Mu COVID variant in the UK – the majority of these from July and August 2021. The figure is broken down as 53 cases in England, 3 in Scotland, 2 in Northern Ireland and 1 in Wales.

The strain has been called VUI-21JUL-01 by Public Health England.

Will vaccines still work against the Mu variant?

There is not yet enough evidence to say conclusively whether the Mu variant will be able to evade protection from coronavirus vaccines.

One study, published on 15 December 2021 by scientists in the USA, tested two doses of the Moderna coronavirus vaccine against infection with the Mu variant. They found that, when compared with no vaccinations, a double jab was 90 per cent effective against Mu.

Another study, published 26 September 2021, tested the effectiveness of the BioNTech-Pfizer vaccine against the Mu variant. The study used samples from people who had been double jabbed, collected one week after their second dose.

Researchers found that while the effectiveness of the Pfizer vaccine was reduced to 79 per cent (compared to 96 per cent effectiveness at neutralising the original COVID-19 strain), it "still possesses adequate ability to neutralise the majority of the [variants]".


What other variants have been identified in the UK?

As of 7 January, there are five strains considered to be ‘of concern’ by PHE, including the Omicron, Delta and Alpha variants.


Amy ArthurEditorial Assistant, BBC Science Focus

Amy is the Editorial Assistant at BBC Science Focus. Her BA degree specialised in science publishing and she has been working as a journalist since graduating in 2018. In 2020, Amy was named Editorial Assistant of the Year by the British Society of Magazine Editors. She looks after all things books, culture and media. Her interests range from natural history and wildlife, to women in STEM and accessibility tech.