Identified for the first time in Colombia in January 2021, present in 39 countries and classified among the Variations of interest (Voi) by the World Health Organization (WHO) on 30 August last, the Mu (B.1.621) and its version advanced (B.1.621.1) were found to be “highly resistant” both to antibodies generated by natural infection with the native virus, that of Wuhan, and to that induced by vaccines. This is indicated by the research coordinated by the Japanese University of Kyoto and online on the bioRxiv website, which hosts the articles awaiting examination by the scientific community.

“We show that the Mu variant is highly resistant to both convalescent sera and individuals vaccinated with BNT162b2,” Pfizer’s Cominarty vaccine, write the Japanese researchers, coordinated by Keiya Uriu and Izumi Kimura, both of the University of Tokyo. In particular, it was observed that the Mu variant is 12.4 times more resistant than the sera of convalescents and 7.5 times compared to those of vaccinated individuals.

“Our results will help to better assess the risk posed by the MU variant for both the vaccinated and those who have had the infection, as well as for the population never exposed to the SarsCoV2 virus.”

The experiments that made it possible to reach these conclusions were conducted using the pseudovirus technique, explains virologist Francesco Broccolo, of the University of Milan Bicocca. “That is, only the Spike protein of the Mu variant and of the other variants with which it was compared was used. This avoids using the whole virus, which would be dangerous”, noted the expert.

This made it possible to calculate the resistance of the variant to natural and vaccine-induced antibodies and to understand, said Broccolo, “that the mutations that make the MU variant particularly aggressive are eight. Among these we note the E484K, the same present in the Beta and Gamma variants, the N501Y also present in the Alfa and the D950N, present in the Delta “. Of these mutations, he continues, “the most important, which seems to reduce sensitivity to vaccines and antibodies, is E484K, identified in the two most feared variants for their ability to evade vaccines”.


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