Delta COVID Variant May 'Squelch' Mu in 'Survival of the Fittest' Struggle

The Mu variant, which the World Health Organization recently deemed a "variant of interest," could be "squelched" by the Delta COVID variant in the U.S., an expert has told Newsweek.

Some attention has recently been diverted away from the Delta variant, which currently accounts for 99 percent of COVID cases in the U.S., by the emergence of the Mu variant of COVID, and the World Health Organization (WHO) and the Centers for Disease Control and Prevention (CDC) describing it as a variant of interest.

Mu has been found in 46 countries, as well as 49 U.S. states, Washington D.C. and Puerto Rico. However, WHO says the variant has not spread as rapidly or efficiently as Delta, which was first observed in India and has since been found in at least 170 countries and spreads at least twice as fast—possibly even four times as fast—is the original COVID-19 strain.

Mu, which is believed to have originated in Colombia, has been selected as a variant of interest because it contains genetic material that could help it evade the antibody protection provided by COVID vaccines.

"Mu has some troubling mutations, but it's not spreading widely in the States," John P. Moore, a professor of microbiology and immunology at Weill Cornell Medical College, told Newsweek. "I've seen very few studies on its properties because it's not been widely studied yet. The key thing is, it's just not spreading much."

Moore went on to explain that the fact Mu isn't spreading as rapidly as Delta may mean that the new variant eventually disappears almost altogether. He pointed to the U.K. as an example, saying that when Delta got a foothold in the country in late 2020 the Alpha variant was almost completely dominated.

"One of the things we've learned with Delta is that it squelched out less transmissible variants," Moore said. "It's the most transmissible variants that dominate. And everything else just becomes less and less of an issue. Unless Mu has unique transmissibility properties, and that would be surprising because it's not been seen so far.

"It's survival of the fittest from the virus perspective."

Moore's comments were reflected by Dr. Mike Ryan, WHO head of health emergencies, during a press conference on Tuesday during a discussion regarding variants such as Mu.

He said: "In some senses, these viruses are competing with themselves, not just with us. Any virus that emerges has got to compete with the 'best of class.'

"At the moment the 'best of class' is the Delta variant so it tends to outcompete other variants."

Echoing Moore, Maria Van Kerkhove, the WHO's COVID-19 technical lead, said at the press conference: "The Delta variant for me is the one that's most concerning because of the increased transmissibility. Where Delta takes hold, it rapidly replaces other viruses circulating.

"Delta is also continuing to evolve. So we are also looking at several sub-lineages of Delta and looking at how the virus might be changing."

With transmissibility being the key to a COVID variant surviving and becoming dominant, the reproductive number (R0) showing how many people an infected person could spread the virus to is key to predicting which variants will become the most concerning.

As an example, influenza has a reproductive number of two, which means that on average every person who gets sick with flu infects two others. The Delta variant, on the other hand, currently has an estimated R0 between 5 and 9, with the CDC putting its R0 at 8.5 in August.

Moore said that the Mu variant hasn't spread enough yet for scientists and health organizations to make a good estimate of its reproductive number. "To come up with that kind of estimate, you need a lot of transmissions. It's got to be transmitted more than it is right now," he said.

With regards to how the public should react to the emergence of Mu and its classification as a variant of interest, Moore was very clear: "get vaccinated."

"Vaccination will protect you against all of these variants no matter its degree of antibody resistance, it will still give you substantial protection," the professor of microbiology and immunology concluded, also emphasizing the need for the continued use of precautionary measures like face masks.

"Mu hasn't acquired a pair of scissors that will cut through masks, or blow away vaccines," he said. "Delta is the problem. And the best way to deal with Delta is to get vaccinated."

Correction 09/15/21, 11:27 a.m. ET: This article was updated to correct the spelling of the Centres for Disease Control and Prevention, Colombia, as well as the number of states in the U.S.