Mu variant: what to know about the latest COVID-19 ‘variant of interest’

Right now delta is the COVID-19 variant on everyone’s minds, but there’s a new variant of the SARS-CoV-2 virus, the virus that causes COVID-19, that has experts, including the World Health Organization (WHO), sitting up and taking notice. That new variant is called mu.

Here’s what you need to know about it:

What is the mu variant? Mu is the most recent significant variant of the SARS-CoV-2 virus. Its official Phylogenetic Assignment of Named Global Outbreak (Pango) lineage designation is B.1.621. According to the World Health Organization, early indicators suggest mu might be better at evading vaccines, antibody treatments, and the natural immunity gained from previous COVID-19 infections. On August 30, the WHO named mu a “variant of interest.”
How is a “variant of interest” different than a “variant of concern?” While the SARS-CoV-2 virus mutates all the time, some mutations become significant because they give the virus new abilities or can impact the human body in new ways. The WHO classifies these significant mutations as either “variants of concern” or “variants of interest.” Alpha, beta, gamma, and delta are the only variants of concern, which means there is ample evidence the variants are more dangerous than the original strain of SARS-CoV-2. Variants of interest, on the other hand—which mu is—are variants that have the potential to increase harm, but more research is needed to confirm this. If increased harm is confirmed, a variant of interest will become an official variant of concern.
What does the WHO say about mu? In its most recent weekly briefing, the WHO states, “the mu variant has a constellation of mutations that indicate potential properties of immune escape. Preliminary data presented to the Virus Evolution Working Group show a reduction in neutralization capacity of convalescent and vaccine sera similar to that seen for the beta variant, but this needs to be confirmed by further studies.”
Where and when was mu first detected? The mu variant was first detected in Colombia in January 2021. It currently makes up 39% of COVID-19 cases in Colombia and 13% of COVID-19 cases in Ecuador.
What countries is mu in now? Mu is currently in at least 39 countries, mainly in South America. However, mu has also been detected in the United States, Europe, and Hong Kong.
Is mu resistant to vaccines? Early signs indicate that vaccines could be less effective against mu than they are against the delta variant (which already reduces vaccines’ effectiveness). However, there aren’t any signs yet that mu is completely resistant to vaccines. And any resistance still needs to be confirmed through further study.