Mu coronavirus variant recorded in 167 people in L.A. County

Crowds of people, some in masks, walk along a sidewalk bordered by palm trees.
People walk in Hermosa Beach on Sunday.
(Francine Orr / Los Angeles Times)

A coronavirus variant recently determined to be a “variant of interest” has been detected in 167 people over the summer in Los Angeles County, officials said.

The variant now known as Mu was mostly detected in July, according to analyses completed between June 19 and Aug. 21, the Department of Public Health said.

Named after the 12th letter of the Greek alphabet, Mu was declared by the World Health Organization as a “variant of interest” on Aug. 30, and was first identified in January in Colombia, the department said. Mu, also known as B.1.621, has since been reported in 39 countries.


The U.S. Centers for Disease Control and Prevention, however, has not labeled Mu a variant of interest.

Variants of interest are not considered as much of a potential threat as so-called “variants of concern,” which include Delta. Delta is now estimated to comprise more than 99% of the variants circulating in the United States. The Delta variant displaced Alpha as the nation’s most dominant strain at the beginning of the summer.

Dr. Anthony Fauci, President Biden’s chief medical advisor for the pandemic, has said Mu is important to monitor, even though it is rarely seen in the United States.

“We’re paying attention to it,” Fauci said at a news briefing last week. “But we don’t consider it an immediate threat right now.”

Mu is different from another variant known as C.1.2, which was recently identified in South Africa. The World Health Organization, however, has not placed C.1.2 on its list of variants of interest or of concern.

A new coronavirus variant has emerged from South Africa. It has a high number of mutations but has a ways to go to challenge Delta.

Sept. 3, 2021


Another variant, Lambda, has also attracted attention recently after being labeled a variant of interest by the World Health Organization in June. Lambda, first documented in Peru in December, is worth watching, some scientists say, because it has had spread widely in South America.

The CDC, however, has not labeled Lambda as a variant of interest.

Lambda is worth watching because of its massive spread in South America, but health officials don’t know whether it will supplant Delta.

Aug. 18, 2021

Dr. Ashish Jha, dean of the Brown University School of Public Health, tweeted that he doubted Mu, Lambda or C.1.2 will displace Delta as the nation’s dominant variant.

“I don’t lose sleep over new variants,” Jha wrote. “I worry about people’s fatigue with the current one.”

Times staff writer Amina Khan contributed to this report.