How dangerous is the Mu variant: this is the last ‘threat’ that clings to the Covid

We have not just emerged from a fifth wave of the coronavirus sponsored by the Delta variant and new ones have already emerged that struggle to leave behind the absolute protagonist of the summer. The last candidates named by the World Health Organization have been Lambda (C.37), considered ‘of interest’ –previous step to be “worrisome”, such as Alpha, Beta or Delta– in June, and Mu, whose appointment was as recently as August 30. A new study warns that the latter can become a serious threat, as its resistance to vaccines is greater than that of Beta.

The article has been published in the BioRxiv platform, a repository of studies that are waiting to be reviewed by independent experts. The work of Japanese researchers from several universities, analyzes the performance of the sera of people who have passed the Covid or have been vaccinated against Mu. “Our results will help to better evaluate the risk offered by the Mu variant for those vaccinated, those previously infected and naïve populations [ni contagiadas ni vacunadas]”the authors state.

The authors manufactured pseudoviruses that included the protein S of Mu or other variants (original, Alpha, Beta, Gamma, Delta, Epsilon and Lambda) and confronted them with the serum (blood plasma containing antibodies) of eight convalescent and ten vaccinated ( with Pfizer-BioNTech). The conclusion? Mu is significantly more resistant than Beta, the strain so far with the greatest escape from neutralization, both in some and in others.

The new variant of interest was 12.4 times more resistant than the original to convalescent serum, while Beta was 8.2 times. Alpha, on the other hand, was only slightly more than double that. With respect to the vaccinated serum, Mu was 7.6 times more resistant, while Beta was 6.3 times.

History of Mu

What is Mu’s secret? Its protein S, which attaches itself to human cells to infect them, contains eight mutations, including some old known ones, such as E484K, already present in Beta and Gamma variants; N501Y, which it shares with Alfa, and D614G, which also includes Delta. “The E484K mutation has been shown to reduce the sensitivity of antibodies induced by infection or vaccination,” the authors write.

However, this variant is not a rookie. It was described for the first time in Colombia at the beginning of the year, where it has been the predominant one since the second half of May, and is currently present in 39 countries. According to the information collected from the Gisaid platform, the benchmark in the global monitoring of the pandemic, was detected in Spain at the end of February and its peak was in June, when it accounted for 4% of the sequenced samples.

Despite the potential danger it poses, the Public Health specialist of the Foundation for the Promotion of Health and Biomedical Research of the Valencian Community (Fisabio), Salvador Peiro, adventure that “Delta us will protect of Mu although this, like Beta, withstands the neutralizing antibodies better “.

The study presented by the Japanese researchers has been carried out in vitro, that is, not with human subjects but only with their serum. And, although this gives a clue to the behavior of the virus, it is not the only factor to take into account when talking about its possible prevalence. Or, as Peiró says, “how it is going to work on the ground is something else: it also needs to be transmitted better and, for now, Delta seems to be winning.”

He explains it. “When there was no selective pressure at the beginning of last year (no lockdowns yet, no vaccines, no people immunized for having passed the Covid), all [las variantes] they could live together quite well. Now [lo hacen] only more suitable for streaming in today’s environment“.

“And Mu, whatever the studios say in vitro, will have to show that it can displace Delta, which, the truth, works very well “when it comes to spreading infections, as we have already seen in the fifth wave.

Although Peiró warns that this is his speculation, he points out that all the countries in which he is found “are reducing transmission, regardless of the predominant variant they have.” In Latin America, where the strain is more present, Delta is displacing other variants, like Gamma. Even in South Africa, where Beta was almost completely dominated, it has already been superseded by Delta. Lambda, the predominant variant in Peru, seems to hold out, for now.

“The strategy for now is to worry about Delta and watch Mu without getting too nervous,” sums up the Public Health specialist. At most, it would be about controlling travel from Colombia. Although, well seen, “the transmission there must be between three and four times less than in Spain, so they would do better to take care of us“he admits sarcastically.

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