CDC, Fauci Keeping 'Close Eye' on Mu Variant but Focused on Delta in U.S.

Federal health officials say they're keeping a "close eye" on a new variant found to be more resistant against COVID-19 vaccines, but are remaining focused on combatting the spread of the Delta variant in the U.S.

"We certainly are aware of the new variants," Dr. Anthony Fauci, the director of the National Institute of Allergy and Infectious Diseases, told reporters on Thursday. "We're keeping a very close on it. It [has been] seen here, but it is not at all even close to being dominant. As you know, the Delta is more than 99 percent dominant."

During the White House coronavirus briefing, Dr. Rochelle Walensky, director of the Centers for Disease Control and Prevention, added: "There have been sequences here [in the U.S.], but again, as Dr. Fauci said, over 99 percent of the sequences we're seeing right now are Delta."

Two days earlier, the World Health Organization (WHO) identified the Mu variant as a new "variant of concern," after the strain was shown to have the potential to evade immunity provided by vaccines and infections alike.

The Mu variant, also known as B.1.621, was first identified in Colombia but has since been confirmed in at least 39 countries.

Although global prevalence of the variant has declined is currently below 0.1 percent, the Mu variant's prevalence in Colombia and Ecuador have consistently increased.

"This variant has a constellation of mutations that suggests that it would invade certain antibodies—not only monoclonal antibodies—but vaccine and convalescent serum induced antibodies," Fauci said on Thursday.

Mu Variant COVID Fauci CDC Walensky
Dr. Rochelle Walensky, director of the Centers for Disease Control and Prevention (CDC), and top infectious disease expert Dr. Anthony Fauci addressed the Mu variant on Thursday. Walesnky and Fauci testify before the Senate Health, Education, Labor, and Pensions Committee July 20, 2021 on Capitol Hill in Washington, DC. J. Scott Applewhite/Pool

The WHO has said the Mu variant would require further studies in order to confirm whether it is more contagious, more deadly or more resistant to vaccine and treatments than other coronavirus strains.

In the meantime, Fauci reassured that the available vaccines would still be relatively effective at preventing severe illness from a new variant like Mu.

"There isn't a lot of clinical data to suggest [increased resistance to antibodies]," Fauci said. "It is mostly a laboratory in vitro data—not to downplay it. We take it very seriously, but remember, even when you have variants that do diminish somewhat the efficacy of vaccines, the vaccine still are quite effective against variants of that type."

"Bottom line: We're paying attention to it. We take everything like that seriously, but we don't consider it an immediate threat right now," he concluded.

The Delta variant remains the dominant strain of the virus in the U.S., making up nearly all new cases and causing an alarming rise in hospitalizations and deaths across the country over recent weeks.

The Delta variant is among four variants of concern in the U.S., alongside the Alpha variant, the Beta variant and the Gamma variant.

The Mu variant currently accounts for 0.2 percent of total cases in the U.S., according to data from the CDC. The only variant that accounts for more than 0.3 percent of circulating cases in the country is the Delta variant, which is responsible for 99.1 percent of cases.