What to know about new mu variant of virus

Scientists are closely tracking the ascendant mu variant, a strain of coronavirus first detected in Central America in January.

The World Health Organization upgraded mu to its “variants of interest” list late last month, a designation given to strains that exhibit alarming mutations. In a statement, the WHO cited preliminary evidence that the latest strain may be able to evade vaccines and antibodies.

But there is “no reason to think mu is scarier than delta, or going to displace delta,” said Dr. Wesley Long, an infectious disease expert and medical director of diagnostic microbiology at Houston Methodist.

Here is what we know:

What is a ‘variant of interest’?

A coronavirus variant of interest shows worrisome genetic changes that can affect the severity of the resulting sickness and how easily the virus is transmitted from per

son to person, according to the WHO.

Such variants have the potential to cause significant community transmission, leading to clusters of infections that pose a big risk to public health.

The WHO tracks emerging strains in two categories. The five current variants of interest — including mu, lambda, kappa, iota and eta — are one step below the more serious “variants of concern” category that includes the original alpha strain and the highly infectious delta strain currently sweeping the globe.

Why is it called ‘mu’?

To avoid stigmatizing regions where new variants emerge, strains are now named after letters in the Greek alphabet. Mu, named after the 12th letter in the ancient alphabet, was designated a WHO ‘variant of interest’ on Aug. 30.

Is mu in Texas?

Mu is present in the state, but it accounts for a tiny fraction of all cases sequenced by scientists.

Delta remains the most dominant strain, accounting for about 99 percent of all cases nationwide and 88 percent globally.

So far, the mu variant has been detected in dozens of countries, according to the WHO, but the largest number of cases remains clustered in Colombia, where it accounts for 39 percent of all cases.

Mu outbreaks are largely “isolated events,” Long said.

Should we be worried?

Much of what scientists know about the mu variant is based on laboratory studies, so it “remains to be determined” whether the strain will spread outside its current clusters or evade vaccines, said Dr. Hana M. El Sahly, a professor of molecular virology and microbiology and infectious diseases at Baylor College.

Delta, first detected in India in October 2020, overtook the alpha strain over an eight-month period to become the dominant variant worldwide by early June, according to data from GISAID. By contrast, it has been about eight months since mu was first detected in Colombia.

“It remains something we need to follow, but so far it has not caused problems” like delta, said El Sahly.

It is unclear how vaccines perform against mu. But preliminary studies at a Pfizer laboratory in Italy showed promise, indicating that the vaccine neutralized the new variant, El Sahly said.

“That gives a degree of reassurance,” she said, “but it is hard to say with certainty.”