What you need to know about Mu, a new variant of Covid interest

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The World Health Organization has said that a variant of the virus that causes Covid-19 which is now responsible for an increasing proportion of cases in Colombia, and which has been detected in 39 countries around the world, is now a “variant of interest”.

Designating the variant with the Greek letter Mu, the agency said early data indicates that the immunity provided by vaccines or by previous infection “may not be as strong against this variant”, although more studies are needed. required.

In a statement, the WHO said Mu, also known as B.1.621, “has been designated as a variant of interest because it has certain mutations that need to be investigated for their potential impact on the body’s immune response. “.

WHO is tracking variants of interest, which have the potential to be more dangerous than other forms of the virus, and variants of concern, which already pose a more serious threat. Mu is one of the five variants of current interest; there are four variations of concern, including Delta.

Mu was first identified in Colombia in January and is now responsible for 39% of cases in that country, according to the WHO. The global prevalence of the variant is low and declining, according to the agency, but in recent weeks it has risen sharply in Colombia and Ecuador, where it now accounts for 13% of sequenced cases.

In a weekly epidemiological update on Covid-19 released Tuesday, the agency said there had been larger outbreaks of Mu in South America and Europe.

“The Mu variant has a constellation of mutations that indicate potential immune evasion properties,” the update states. He said early data suggested that the ability of blood sera from vaccinated people and people who have recovered from Covid-19 infections to neutralize the Mu variant was similar to their ability against the beta variant, also known as South African variant name, which is particularly evasive of immune responses.

Mu’s reports have been widespread in recent months. In late July, Florida TV station WPLG reported that the variant now known as Mu was responsible for 10% of the Covid-19 samples sequenced in a University of Miami lab. In early August, Reuters reported that seven fully vaccinated residents of a Belgian nursing home had died from an outbreak of B.1.621.

The US Centers for Disease Control and Prevention does not yet list Mu as a variant of interest or a variant of concern, although the European Center for Disease Prevention and Control has already listed it as a variant of interest. . ECDC, an agency of the European Union, says there is evidence that mutations in the variant now known as Mu have an impact on transmissibility and immunity.

Mu is the first new variant to be added to the WHO Variants of Interest list since Lambda was added in June. Delta, the most recently added variant of concern, was upgraded to this status in early May.

“WHO will closely monitor the epidemiological development of this variant, as well as studies on its impact,” the agency said.

Write to Josh Nathan-Kazis at [email protected]