The vanishing variants: Lessons from gamma, iota and mu

In early 2021, scientists in Colombia discovered a worrisome new coronavirus variant. This variant, eventually known as mu, had several troubling mutations that experts believed could help it evade the immune system’s defenses.

Over the following months, mu spread swiftly in Colombia, fueling a new surge of COVID-19 cases. By the end of August, it had been detected in dozens of countries, and the World Health Organization had designated it a “variant of interest.”

“Mu was starting to make some noise globally,” said Joseph Fauver, a genomic epidemiologist at the University of Nebraska Medical Center and an author of a recent study on the variant.

And then it fizzled. Today, the variant has all but vanished.

For every delta or omicron there is a gamma, iota or mu, variants that drove local surges but never swept to global dominance. And while understanding omicron remains a critical public health priority, there are lessons to be learned from these lesser lineages, experts say.

“This virus has no incentive to stop adapting and evolving,” said Joel Wertheim, a molecular epidemiologist at the University of California, San Diego. “And seeing how it did that in the past will help us prepare for what it might do in the future.”