Evaluating the New Mu Variant in California

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A waiter serving a customer a beer during a July performance in San Francisco, as the delta variant began to drive another surge. Scientists and public health officials are now keeping an eye on the next variant of interest, named mu. (Justin Sullivan/Getty Images)

The delta variant pretty much ruined summer by setting back the pandemic recovery by months. So if the public is feeling wary of any new coronavirus variants, it’s understandable.

The latest new strain, called mu, after the Greek letter, is now present in California, with 348 cases having been identified.

Dr. Peter Chin-Hong, an infectious disease specialist at UCSF, joined KQED's Raquel Maria Dillon this week to discuss this new variant and how much of a risk it is to prolonging the pandemic.

The following has been edited for length and clarity.

Why are epidemiologists watching mu so closely?

Chin-Hong: It kind of took over the landscape of viruses in Colombia. In the last month or so, it accounted for up to 40% of cases there and also surrounding countries like Ecuador. And now it may be even higher in Colombia; some estimates are above 90%. Nevertheless, it hasn't really taken off around the world, making up less than 1% of cases around the world. In fact, in the United States, it’s 0.1-0.2% of the cases sequenced last month.

When should we start to worry about a new variant?

I think about three questions that I ask myself every time there's a new variant. Is it more transmissible? Is it more vaccine-evading or vaccine resistant? And does it make you sicker compared to the regular COVID? Personally, what I look at is tempo. If you remember with delta, it took us by surprise. It was found to be so transmissible in taking over the landscape at a tempo that was breathtaking. In May, it was 5% of cases in California. The next month, it started to go to 25%, then 50%. We are not really seeing that with mu outside of Colombia at this moment.

What’s your personal assessment of mu? And is it here in the Bay Area?

Mu is definitely here. It's in 45 countries and in all of the states in the U.S. It's here because there's a lot of travel back and forth between the northern part of South America, where it's dominant, and California.

I'm not dispensing with it; it's something to watch. I'm also not losing sleep over it. These variants may look scary in the lab. But when they come on to the boxing ring that is life, they all play off against each other. And so far, delta is very, very dominant. It's bullyish. It's keeping all these other variants in subjugation.

Are we going to have to be on guard against new variants forever and ever?

Yes, unfortunately, until more of us get vaccinated. SARS-CoV-2, the virus itself, isn't very precise; it’s like it's using a cheap photocopy machine to make copies of itself. Every time it makes a copy, there's a little bit of an error in it, like a smudge. And that smudge may confer new superpowers — that’s a new variant being created. Every time it makes a copy, there's that possibility of mutation. In fact, scientists believe every two weeks there's a new variant somewhere in the world being created, but only a few rise to the rogues gallery of fame, like delta, like mu, like lamda.


We’ve heard that viruses generally evolve to be less deadly and more contagious. Is that going to be true with COVID-19?

The virus has to survive in some way; it doesn't want to die off completely. So some of these superpowers the variants have are probably going to attenuate. These powers of the new variants have been selected for the variants to be prevalent in the community, but not necessarily to be super lethal and kill off all the hosts. So it gets to the point that we want to probably live with COVID, learn to manage it rather than to fear it.

Should we jump every time a variant gets an official letter, or should we just chill out?

I definitely think we have to pay attention to each one of them. I think we have to anticipate, be prepared. It's exhausting, but we have to be in this state of readiness. It reminds us that we're living with this virus and we need to engage in conversations with folks who haven't been vaccinated. Really, vaccination is a powerful ally as we battle mu, iota, delta, lambda, the future variants that don't even have Greek letters yet.

I like your superpower metaphor, but what I really want is for the vaccines to grant me superpowers …

I know, but the vaccines are giving us superpowers. So I think we just have to believe in them more as a country overall.