Photo/Illutration A health care worker fills a syringe with a COVID-19 vaccine at a hospital in Kamagaya, Chiba Prefecture, on July 13. (Asahi Shimbun file photo)

The new Mu variant of the novel coronavirus is more than seven times more resistant to antibodies created by vaccinations than the original strain of the virus, a study by a Japanese research team has found.

Despite the increased resistance, “the Mu variant does not make vaccines ineffective, nor does it require new anti-virus measures at the individual level,” said Kei Sato, an associate professor of virology at the University of Tokyo’s Institute of Medical Science (IMS) and a member of the team.

“(But) we found that the variant is the most resistant to antibodies among the previously detected strains of the virus,” he added. “It’s crucial to identify what types of variants are spreading. That will require an expansion of capacity to conduct genome analyses, which can provide detailed genetic information of the virus.”

The World Health Organization has added the Mu variant, first detected in Colombia, to the list of mutated strains of the virus that it monitors and tracks the spread of.

In the study, a team of researchers from the University of Tokyo’s IMS and other institutions attached a spike protein, which sticks out from the surface of the virus and infects human cells, to the surface of another virus that can be more easily handled than the actual coronavirus.

The researchers repeated the process to generate "pseudoviruses" harboring spike proteins of various mutated strains of the virus and tested how far neutralizing antibodies collected from people inoculated against COVID-19 could prevent the pseudoviruses from entering cells prepared for the study.

The Mu variant was more likely to reduce the effectiveness of antibodies produced from vaccinations than other strains of the virus, the team's results showed. But some of the immunity acquired through inoculations work by different mechanisms from that of antibodies.

The WHO on Aug. 30 designated the Mu variant as a variant of interest. The health ministry subsequently announced that the variant was detected in two travelers from abroad at airport quarantine checks in Japan.

The Delta variant, which is raging across the globe, is designated as a variant of concern, one notch above the variant of interest category.

The team published its findings on Sept. 7, prior to the study being peer-reviewed. It can be viewed at: (https://www.biorxiv.org/content/10.1101/2021.09.06.459005v1.full)

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