The Mu variant has the potential to become immune to vaccine and antibody protection
The World Health Organization has added another strain of coronavirus to its list of “variants of interest”, ie, those that should be monitored because they are likely to escape the immunity provided by vaccines or by antibodies produced after infection.
It is the Mu variant, also known as B.1.621, which entered the WHO watch list on Monday, August 30, after being detected in 39 countries and appearing to be less susceptible to the protection offered by immunizers.
“The Mu variant has a number of mutations that indicate potential immune-evading properties,” reports the WHO weekly bulletin on the pandemic.
According to the report, preliminary data suggest that the new version of SARS-CoV-2 can evade immune defenses in a similar way to the Beta variant, first discovered in South Africa.
The Mu variant was first identified in January 2021 in Colombia. Since then, sporadic cases and some larger outbreaks have been reported around the world. In addition to South America, new infections caused by the variant have been reported in the United Kingdom, Europe, United States and Hong Kong. Although it accounts for less than 0.1% of Covid-19 infections worldwide, it may be gaining traction in Colombia and Ecuador, where it accounts for 39% and 13% of the disease cases, respectively.
Scientists are concerned about whether the variant is more transmissible or leads to more severe forms of the disease than the Delta variant, which is now prevalent across much of the globe.
“The epidemiology of the Mu variant in South America, particularly with the co-circulation of the Delta variant, will be monitored for changes,” states the WHO bulletin.
In the UK, at least 32 cases of the new variant disease have been reported, where the pattern of infections suggests that it was brought in by travelers on several occasions.
A Public Health England (PHE) survey in July said the majority were found in London and in people in their 20s, some already vaccinated with one or two doses of the Covid-19 immunizer.
Also added to the PHE investigation list, Mu is designated as VUI-21JUL-01, which means the variant will be monitored to see how it behaves.
So far, it hasn’t raised as much fanfare as Alpha and Delta, which are rated more severe, in large part because of their greater transmissibility and evading immune defenses.
“At the moment, there is no evidence that VUI-21JUL-01 is outperforming the Delta variant and it seems unlikely to be more transmissible,” the report states, though it cautions: “Immune leakage may contribute to future growth changes.”
A preliminary risk assessment of the Mu variant released by PHE in August highlighted laboratory work suggesting that the variant is at least as resistant as the Beta variant to immunity from vaccination. But more evidence from other studies and real cases is needed.
The degree of threat it poses is uncertain and will depend on new cases in the coming weeks or months, and will increase substantially, especially with the presence of the rapidly spreading Delta variant.
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