Tracking the mu variant

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

Citing preliminary evidence that mu may be able to evade vaccines and antibodies, the World Health Organization upgraded mu to its “variants of interest” list last month.

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.

A coronavirus variant of interest shows worrisome genetic changes that can affect the severity of illness and ease of transmission, 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 highly infectious delta.

Delta remains the most dominant strain, accounting for about 99 percent of all cases nationwide and 88 percent globally. While mu has been detected in dozens of countries, the largest number of cases remain clustered in Colombia, where it accounts for 39 percent of all cases.

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

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.

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