PHE says it has spotted 53 cases of 'Mu' Covid variant in UK which is feared to be resistant to vaccines and is already spreading in 49 US states
More than 50 Britons have been infected with the 'Mu' Covid variant which experts fear blunts the effect of vaccines and is already spreading in all but one US state.
Public Health England said it had spotted 53 cases of the mutant strain — which emerged in Colombia — and that it was first detected in Britain in May.
Scientists believe that while Mu is more transmissible than the original virus, it does not appear to be infectious enough to outcompete the Delta variant.
Delta was first detected in Britain in late March and had become dominant by May, for comparison.
Professor Lawrence Young, a virologist at Warwick Medical School, said he believed Delta represented 'peak infectiousness' for Covid and would be 'very, very surprised' if Mu or any other strain was even more transmissible.
But he warned Mu's vaccine-resistance may make it a future threat, telling MailOnline: 'We may have reached peak infectiousness with the Delta variant and what we have not reached, of course, is peak immune avoidance.'
No-one in the UK had died from Mu by the most recent count on August 30, but five people were admitted to hospital with it. It's unclear how many of these were vaccinated.
PHE sources told MailOnline today they were 'not concerned' about the mutant virus, although its rapid spread in the US has led to growing concerns globally.
Mu has already been reported in every state except Nebraska, with Florida and California recording the highest numbers at 384 cases each. In total about 1,750 Americans have been infected with the virus, according to data.
The variant was responsible for Colombia's deadly third infection wave between April and June, when at the peak 700 Colombians were dying per day. But the outbreak has since subsided.
PHE has admitted the strain, also known as B.1.621, has some ability to evade jabs but the agency has taken confidence from the fact it is not rapidly growing.
A source said: 'This is not really one we are hugely concerned about at this point in time.
'We would want to see t growing in the real world before classifying it as a 'variant of concern', and that is not really happening at the moment.'
The above graph shows cases of the mutant strain in the UK since May (black line - average percentage of cases down to the variant per week, and pink area - the range for the percentage). It reveals that they have remained at very low numbers, making up less than 0.1 per cent of all infections checked for variants. PHE sources told MailOnline they were not 'hugely concerned' by the variant
The above graph shows cases of the 'Mu' variant detected globally. The average number of cases peaked (black line) in mid-July before falling
The above graph shows cases of the mutant strain in the US since April. Its prevalence peaked in May, before cases began to decline amid the spread of the Delta variant (black line, average percentage of cases sparked by the variant)
More than 4,000 cases of the variant have been detected to date and it has spread to more than 40 countries
Mu was determined a 'variant of interest' by the World Health Organization last week. But despite spreading into nearly every state in the US the variant is still at very low numbers, and accounts for 0.2 per cent of all cases in the worst-hit state of California.
It is unclear how infectious Mu is but its mutations to the spike protein suggest it is more infectious than the original virus, but may not rival the dominant Delta strain.
However, it does possess the E484K which is present on the South African 'Beta' variant, which is thought to be the most vaccine resistant strain currently circulating.
Experts have been keeping a close eye on Beta, and fear it could be the next strain to take off in a highly vaccinated population where it would have an evolutionary edge.
Professor Francois Balloux, the director of the Genetics Institute at University College London, told MailOnline he 'would not put money on' Mu taking off in the UK.The WHO currently lists four Covid variants of concern — Alpha, Beta, Gamma and the highly-transmissible Delta.
Mu is the fifth variant of interest and is being tracked alongside Eta, Iota, Kappa and Lambda.
It comes after a report by PHE published at the start of August suggested Covid jabs may be 'less effective' against the mutant strain.
But they said their findings were based on preliminary laboratory evidence, so data was 'very limited and more research is required'.
Their report added that there was 'no evidence' to suggest the variant is more transmissible than the Delta strain.
The report said: 'The level of threat from such a variant depends on its growth and expansion.
'There is very low certainty around growth estimates at present, however in the current context there is no indication that it is out-competing Delta.'
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