No, the mu variant is not the dominant COVID-19 strain in the US

In January, the mu variant of COVID-19 was first detected in Colombia. It has since been confirmed in dozens of countries, including the United States. 

On Aug. 30, the World Health Organization (WHO) labeled the mu variant as a “variant of interest,” which is defined by the global public health agency as variants that have been identified to cause “significant community transmission or multiple COVID-19 clusters.” According to the WHO, the mu variant has exhibited signs of possible resistance to vaccines. 

In the United States, where the highly transmissible delta variant of COVID-19 continues to spread rapidly across the country, VERIFY viewer Craig wants to know how concerned Americans should be about the mu variant.

THE QUESTION

Is the mu variant the dominant COVID-19 strain in the U.S.? 

THE SOURCES

• U.S. Centers for Disease Control and Prevention (CDC)
• World Health Organization (WHO)
• White House
• GISAID
• Nextstrain
• Dr. Anthony Fauci, Director of National Institute of Allergy and Infectious Diseases

THE ANSWER

No, the mu variant is not the dominant COVID-19 strain in the U.S.

WHAT WE FOUND

The U.S. Centers for Disease Control and Prevention (CDC) says on its website that while the WHO classified the mu variant as a “variant of interest” globally on Aug. 30, it has not escalated the mu variant to a “variant of interest” in the United States because it reached its peak in the U.S. in late June and has steadily decreased since then. 

As of Sept. 14, the mu variant accounts for less than 1% of all COVID-19 infections in the U.S., according to the GISAID Initiative, which is an organization that promotes the rapid sharing of data from all influenza viruses and COVID-19. It is still the dominant strain of COVID-19 in Colombia, where it was originally found. 

Meanwhile, the CDC says the delta variant is the “predominant variant” of the virus in the U.S. It currently accounts for 99% of new COVID-19 cases in the country, and roughly 88% of cases globally, according to data from the CDC and Nextstrain, an open-source pathogen-tracking service.  

In a Sept. 2 press briefing by the White House COVID-⁠19 Response Team, a reporter asked public health officials if they were concerned about the mu variant in the U.S. Dr. Anthony Fauci, who serves as the director of the National Institute of Allergy and Infectious Diseases, said the mu variant is not considered an immediate threat right now in the U.S. because it has rarely been seen in the country but noted that they are “keeping a very close eye on it.” 

“This variant has a constellation of mutations that suggests that it would evade certain antibodies — not only monoclonal antibodies but vaccine and convalescent serum-induced antibodies — but there isn’t a lot of clinical data to suggest that. It is mostly laboratory, in vitro data. Not to downplay it; we take it very seriously,” said Dr. Fauci. “But remember, even when you have variants that do diminish, somewhat, the efficacy of a vaccine — the vaccines still are quite effective against variants of that type.” 

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