More than 50 Britons have been infected with the ‘Mu’ Covid variant which experts fear is resistant to vaccines, official data shows.
Public Health England said it had detected 53 cases of the mutant strain after it first cropped up in the UK in May.
No-one had died from the variant by the most recent count on August 30, but five people have been admitted to hospital with it.
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 384 cases each.
In total about 1,750 Americans have been infected with the virus, but it’s not clear how many were hospitalised.
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 told MailOnline: ‘This is not really one we are hugely concerned about at this point in time.’
Despite spreading into nearly every state in the US the varaint is still at very low numbers, and accounts for 0.2 per cent of all cases in the worst-hit area 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.
It was determined a ‘variant of interest’ by the World Health Organization last week.
The above graph shows cases of the mutant strain in the UK since June (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
More than 4,000 cases of B.1.621 have been spotted globally, and it has spread to more than 40 countries.
It was first detected in Colombia in January this year, where sequencing suggests it still makes up the majority of cases.
But across the world cases of the mutant strain are not surging, indicating it may be less of a threat than first feared.
What is the variant ‘Mu’ or B.1.621?
Where have the cases been detected?
This mutant strain was first spotted in Colombia in January.
It has since spread to more than 40 countries including the UK, US, France, Japan and Canada.
Is it increasing in prevalence?
There have been 4,315 cases detected to date, but this is thought to be an underestimate because many countries that have suffered outbreaks do very little surveillance for variants.
The number of cases blamed on the variant declined globally last month, amid the spread of the Delta strain.
It has been detected in every US state except Nebraska, but disease experts in the country say these cases are in very low numbers and it is not likely to outcompete Delta.
In Colombia — where it was first detected — it is still behind around six in ten infections.
Can the strain dodge vaccine triggered immunity?
The variant carries the mutation E484K, which can help it escape antibodies.
This change is also found on the South African ‘Beta’ variant and Brazilian ‘Gamma’ variant.
A PHE study previously suggested it could make vaccines less effective. But UK health chiefs said more research was needed.
It peaked in mid-July making up 0.7 per cent of cases globally, but now makes up less than 0.1 per cent of infections checked for variants.
PHE designated the variant ‘under investigation’ in July, but has not seen the outbreak grow rapidly.
It detected only 5 new cases in the week to August 25, the latest available, taking the total number of infections to 53.
PHE sources pointed out that the high number of cases in the UK meant that only 10 to 20 per cent of them were now being checked for variants.
But they said that whenever a mutant strain ‘under investigation’ is identified, they also sequence the close contacts of that case to check whether it is spreading.
Dr Anthony Fauci, a diseases expert in the US, has said he is not concerned by its spread in the country and that it will not become the next dominant strain.
‘Even though it has not in essence taken hold to any extent here we always pay attention to variants at all times,’ he said.
‘We don’t consider it an immediate threat right now.’
The B.1.621 mutant strain and its sister lineage B.1.621.1 have been detected in every US state except Nebraska, data from outbreak.info shows.
B.1.621’s key mutations include E484K, which can help it escape antibodies and is also found on the Beta and Gamma variants.
It also has the N501Y, which could help it spread easier. This mutation is also present in Alpha.
The coronavirus, called SARS-CoV-2, is mutating all the time as a result of genetic errors when it multiplies. Most mutations are harmless.
But ones that make it able to spread quicker or to survive longer inside the human body are the ones that are likely to stick around.
The World Health Organization said in its report last week: ‘
‘Since its first identification in Colombia in January 2021, there have been a few sporadic reports of cases of the Mu variant and some larger outbreaks have been reported from other countries in South America and in Europe.
‘Although the global prevalence of the Mu variant among sequenced cases has declined and is currently below 0.1 per cent, the prevalence in Colombia (39 per cent) and Ecuador (13 per cent) has consistently increased.
‘The epidemiology of the Mu variant in South America, particularly with the co-circulation of the Delta variant, will be monitored for changes.’
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.’