COVID-19’s new mu variant: 8 things to know

The highly contagious delta variant continues to be the most dominant strain of the SARS-CoV-2 virus, causing thousands of new COVID-19 infections daily around the globe.

But a new strain has also emerged on the scene: the mu variant. We asked infectious diseases specialist and head of Internal Medicine David Tweardy, M.D., for details about this new COVID-19 mutation. Here’s what he had to say.

So, what do we know right now about the mu variant?

It first emerged in Colombia in January 2021, and it quickly became the dominant strain there.

Where else has it been found?

It spread through South America first, but eventually made its way to 40 or 50 other countries. It’s still most prevalent in South America, but a few cases have also been reported in the U.S., the United Kingdom, and other places in Europe, so you could certainly say that it’s gone global. Still, it’s only considered a variant of interest at this point, rather than a variant of concern.

What’s the difference between a “variant of interest” and a “variant of concern?”

A mutation becomes a “variant of interest” when it emerges and becomes the dominant strain in a particular geographical area. That status gets elevated to a “variant of concern” when the mutation not only starts being found outside its country of origin, but also becomes the dominant strain in those areas.

How does the mu variant stack up against the delta variant?

There’s still very little published data, but the reports I’ve seen indicate that the mu variant may only be about 20% more infectious than the original Wuhan virus. That’s good news, since the alpha variant is 50% more infectious and the delta variant is 100% more infectious than the original.

In fact, the news gets even better. Because in some places where the mu variant has been found, it’s actually becoming less prevalent.

In South America, for instance, where it was first detected and identified, it peaked in July, with just 6% of all cases there. Now, two months later, it’s down to 3%. Most of the other cases there are attributed to delta. Similarly, at the global level, mu infections appear to have peaked in mid-July at 0.6% of new infections; now mu infections represent only 0.1% of new infections worldwide. So, mu is going in the opposite direction. And that’s really great, if you’re concerned at all about what the next wave might be after delta.

Will the vaccines currently available offer protection against the mu variant?

The mu variant’s sequencing indicates it has features that could still make it infectious to people who have either natural immunity due to a previous COVID-19 infection or acquired immunity due to vaccination.

One study out of Japan suggested that serum antibodies from people with immunity acquired from either infection or vaccination are five times less effective at neutralizing the mu variant than the original strain. Another study in Italy only found them to be two times less effective. Both are cause for concern, but it’s not clear yet if that two-fold difference is biologically important. A five-fold difference could be. So, I’d like to see a tie-breaker.

But in order to obtain that data, people actually have to be exposed to the mu variant. And the likelihood of that is still fairly low, since it’s not nearly as prevalent or infectious as the delta variant. People are far more likely to be exposed to and infected with the delta variant right now. It makes up the vast majority of cases worldwide.

What should people do to protect themselves against the mu variant?

There’s nothing people could be doing right now that’s any different from anything they’ve already been doing to guard against other variants and viruses.

• Get vaccinated against COVID-19 as soon as possible, if you haven’t already, and encourage those around you to do the same.
• Keep masking up in public spaces.
• Avoid crowds and maintain social distancing.
• Practice good hand hygiene.

What about cancer patients and immunocompromised individuals? Any special guidance for them to protect against mu or other new COVID-19 variants?

The same guidance applies. But if you’re in cancer treatment and you’re not already vaccinated, talk to your care team about the best time to get vaccinated. And, if you are vaccinated, get your third dose as soon as you’re eligible to. Even if your immune response is far less than the average person’s, it’s still better to have some protection than none.

What’s the most important thing to keep in mind about the mu variant?

The news is actually pretty good, in terms of prevalence. Because based on the data we have so far, the mu variant seems to already be disappearing, not emerging.

Schedule a COVID-19 vaccine appointment at MD Anderson. Appointments are open to patients, caregivers and the general public.

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