Mu COVID Variant, Possibly Vaccine-Resistant, Most Prevalent in These U.S. States

The Mu variant of COVID is particularly prevalent in certain states of the U.S. and at least one case has been detected in every state except one.

As of September 4, the state with the highest proportion of Mu cases was Alaska, where 146 Mu cases have been sequenced, according to the variant tracker. This translates to a prevalence of about four percent.

The Virgin Islands follow, with six cases sequenced—a prevalence of about three percent.

Hawaii, Maine and Connecticut then follow, with 39, 42, and 73 Mu cases sequenced, each with a prevalence of about one percent.

The data site also showed that the only state Mu had not been sequenced in was Nebraska. collects its data from the GISAID database which enables rapid sharing of influenza virus data as well as COVID.

It comes after infectious disease expert Dr. Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases (NIAID), said in a White House COVID press briefing last week that the variant had mutations that suggests it "would evade certain antibodies," including antibodies provided by vaccines.

That said, Fauci added that there isn't a lot of clinical data on Mu at the moment and said that even if Mu is slightly vaccine resistant, "vaccines still are quite effective against variants of that type."

He concluded that U.S. health officials were "paying attention" to Mu but "don't consider it an immediate threat right now."

In any case Mu is far from dominant in the U.S. right now. The most recent Centers for Disease Control and Prevention (CDC) data shows that the Delta variant is by far the most prevalent COVID variant in the country, accounting for more than 99 percent of cases sequenced in the week ending August 28.

At that time, Mu, also known as B.1.621, accounted for just 0.2 percent of cases and had not been declared a Variant of Interest (VOI) yet.

The World Health Organization classified Mu as a VOI on August 30, describing it as having "a constellation of mutations that indicate potential properties of immune escape."

The variant was first identified in Colombia in January 2021, and there have been sporadic reports of outbreaks in other countries since then. As of August 29 there had been more than 4,500 sequences of Mu reported from 39 countries, the WHO said in its weekly update from August 31.

While global prevalence was low at the time—less than 0.1 percent—prevalence in Colombia was much higher at 39 percent and also in Ecuador at 13 percent.

COVID testing
A lab technician isolates COVID samples at a diagnostics facility in Texas, August 13, 2021. Health officials are tracking the Mu variant, which has been found across the U.S. Brandon Bell/Getty