More Data Point to COVID-19 Mu Variant’s Antibody Resistance


Researchers found the mu variant to be the most resistant variant to antibodies from either previous infection or from vaccines, a spot that had been previously occupied by the beta, or the South African, variant.

Best to start with the caveats and limitations. It’s a small study, utilizing the antibodies of 18 people who’ve either gotten COVID-19 and recovered, or who’ve been vaccinated against SARS-CoV-2. It’s preprint so it hasn’t yet been subjected to the rigorous examination that studies in peer-reviewed journals undergo.

The preprint study does, however, underscore that medical experts want to keep a close eye on the mu variant of COVID-19, which has raised concerns about its capability to escape antibodies created either through previous infection or vaccinations. Those concerns should be taken seriously, according to investigators with the Institute of Medical Science at the University of Tokyo.

“Since breakthrough infection by newly emerging variants is a major concern during the current COVID-19 pandemic … we believe that our findings are of significant public health interest,” they state in their study, which was posted on bioRxiv, an open access repository for preprint studies. “Our results will help to better assess the risk posed by the mu variant for vaccinated, previously infected and naïve populations.”

Despite the small size of the study, investigators did reach some troubling conclusions. They found the mu variant to be the most resistant variant to antibodies from either previous infection or from vaccines, a spot that had been previously occupied by the beta, or South African, variant. However, they stress that their findings do not imply that COVID-19 vaccines would be ineffective against the mu variant.

Source: World Health Organization

Source: World Health Organization

To reach their conclusions, investigators created pseudoviruses—copies of the various COVID-19 variants—and set them loose upon the antibodies extracted from the 18 participants.

Kei Sato, PhD, a professor at the Institute of Medical Science at the University of Tokyo and the study’s lead author, admits that the study’s findings would have carried more weight if investigators had used real variants, rather than pseudoviruses. Still, Sato tells Newsweek that pseudovirus data are physiologically relevant, nonetheless.

Francesca L. Beaudoin, MD, MS, PhD, interim chairwoman of epidemiology at the Brown University School of Public Health, says that the findings should spur further research about mu, but does question the use of pseudoviruses. She tells Newsweek that “we don’t know if reduced response to antibodies in an artificial laboratory setting is correlated with clinical disease.” She also underscores that “this was a small study and sometimes results observed in a small sample are due to chance findings.”

Kei Sato, PhD

Kei Sato, PhD

At this point there doesn’t seem to be any danger of mu shoving delta aside to become the dominant variant.

“We just showed the sensitivity of mu variant,” Sato tells Newsweek. “We neither talked about mu’s transmissibility nor say that the mu will outcompete delta.”

That’s actually a good thing, despite the fact that delta currently fuels the COVID-19 surge in the United States. Studies released by the Centers for Disease Control and Prevention (CDC) last Friday indicate that the COVID-19 vaccines are effective against the delta variant and that individuals who’ve been vaccinated are 11 times less likely to die because of COVID-19 than unvaccinated individuals.

Davey Smith, MD, MAS, the head of the division of infectious diseases and global public health at the University of California San Diego, who was not involved in the study, tells Newsweek that “we already know that delta has out-competed beta, so the virus that ‘wins’ is not necessarily the one that is least neutralizable."

Investigators with the Institute of Medical Science at the University of Tokyo write in their study that “we demonstrate that the mu variant is highly resistant to sera from COVID-19 convalescents and BNT162b2-vaccinated individuals. Direct comparison of different SARS-CoV-2 spike proteins revealed that mu spike is more resistant to serum-mediated neutralization than all other currently recognized variants of interest (VOI) and concern (VOC). This includes the beta variant (B.1.351) that has been suggested to represent the most resistant variant to convalescent and vaccinated sera to date….”

Smith said that the study “looks to be scientifically rigorous; however, the number of people who had their blood tested, 18 total, is rather small. I bet the journal will ask for more samples tested.”

This not the first time that Sato has been involved in a study that looks at COVID-19 variants. Infection Control Today® reported in July about a study Sato led that examined the potential lethality of the lambda variant. That preprint study found that 2 mutations in the lambda variant—T76I and L452Q—makes it more infectious than the D614G variant, the so-called wild type. The August lambda study stated that “the RSYLTPGD246-253N mutation, a unique 7-amino-acid deletion mutation in the N-terminal domain of the lambda spike protein, is responsible for evasion from neutralizing antibodies.”

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