Delta COVID Variant Could Still Dominate Despite Mu Study Showing Antibody Resistance

A preliminary study highlighting the potential resistance of the Mu COVID-19 variant to antibodies has been released as scientists continue to keep an eye on the mutant virus.

The study, published by researchers at the Institute of Medical Science at the University of Tokyo and other Japanese institutions, compared Mu to other variants of COVID-19 to observe how they reacted to human defences, either by natural immunity due to a previous infection, or to vaccine-induced immunity.

To do this, the researchers created a pseudovirus—a sort of model copy—of various COVID-19 variants and subjected them to the antibodies of 18 people who had either had COVID-19 before or had been vaccinated.

They found that the Mu variant was even more resistant to the serum antibodies than all the other currently recognized variants, including Beta, which the study said "was thought to be the most resistant variant to date."

However, there are a couple of details to be noted.

The study is a pre-print, meaning it has not yet undergone the rigorous scrutiny of other scientists that is required before it can be published in a medical journal. Pre-print studies should therefore be read with caution.

Secondly, the study was small, according to Dr Davey Smith, 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.

He told Newsweek: "It 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."

Another limitation is that the observations are from pseudoviruses as opposed to live viruses, said Kei Sato, a professor at the Institute of Medical Science at the University of Tokyo and the study's lead author.

He told Newsweek that validation using live viruses would be important in future investigation, though he added that pseudovirus data is still physiologically relevant.

What the study doesn't mean is that Mu is about to overtake Delta as the dominant virus in the U.S., for example. "We just showed the sensitivity of Mu variant," said Sato. "We neither talked about Mu's transmissibility nor say that the Mu will outcompete Delta."

What's more, the resistance of a variant to antibodies is not the only factor that allows it to proliferate. "We already know that Delta has out-competed Beta," said Smith, "so the virus that 'wins' is not necessarily the one that is least neutralizable."

Crucially, the study also doesn't mean that COVID-19 vaccines are not effective against Mu, Sato stressed. He told Newsweek that vaccines would still be effective even against Mu despite its apparent resistance.

Mu was only added to the World Health Organization's Variant of Interest (VOI) list late last month, and data is still coming together .

Results in a laboratory do not always reflect real life, said Dr Francesca L. Beaudoin, Interim Chair of Epidemiology at the Brown University School of Public Health.

She said the preliminary results from the Mu study support further research on Mu as a VOI, but that it would be too early to base policy decisions off of.

"We don't know if reduced response to antibodies in an artificial laboratory setting is correlated with clinical disease," she told Newsweek. "Lastly, this was a small study and sometimes results observed in a small sample are due to chance findings."

Lab technician
A stock image shows a lab technician at work with samples. A Mu variant study looked at how resistant the variant may be to antibodies. appledesign/Getty