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  • The World Health Organization (WHO) has designated Mu variant COVID-19 a variant of interest.
  • This means specific genetic markers have developed that could make it more infectious or able to evade vaccine protection.
  • Though there are few cases of COVID-19 related to the Mu variant, this could change if the variant is more infectious than the Delta variant.

The World Health Organization (WHO) has added another COVID-19 variant to the variants of interest (VOI) list. It’s called Mu.

Experts say the genetic changes in this variant may make it more infectious and capable of evading the protection granted by vaccination.

The WHO added Mu to its variant of interest list at the end of August. Mu, also known as B.1.621, was first identified in Colombia in January but is now found in over 40 countries.

“Since its first identification in Colombia in January 2021, there have been a few sporadic reports of cases of the Mu variant, and some larger outbreaks have been reported from other countries in South America and in Europe,” the WHO wrote in a recent COVID-19 update.

According to, a database operated by Scripps Research, the United States has identified more than 2,000 cases of Mu variant COVID-19, with almost 400 in California and roughly half that amount in New York.

The Centers for Disease Control and Prevention (CDC) estimates that 0.1 percent of COVID-19 cases in the United States are the Mu variant. Still, that number could grow quickly if it is more infectious, similar to how the Delta variant became widespread.

“All viruses, including SARS-CoV-2, evolve over time through mutations that occur during replication,” Hannah Newman, MPH, CIC, director of Epidemiology at Lenox Hill Hospital in New York, told Healthline.

“Most changes are inconsequential to the transmissibility and virulence of the virus itself,” she explained. “However, sometimes these changes will affect the severity of disease, how easily it spreads, and protection from the vaccine.”

She added that these changes have been closely monitored since the beginning of the pandemic and are designated variants of interest (VOI), variants of concern (VOC), and variants of high consequence (VHC).

“An emerging variant is labeled as a variant of interest when specific genetic markers develop that have the potential to be more concerning,” she said. “This is basically sounding the alarm saying, ‘We should really keep an eye on this and see where it goes.’”

Recent research found the Mu variant’s potential to be more infectious comes from 17 mutations it shares with other variants associated with increased transmissibility, evading antibodies generated by COVID-19 vaccines, and suppression of our immune response.

This ability to evade natural or vaccine-induced protection is called immune escape.

“Immune escape means that the virus is inclined to not be able to be detected by the body’s immune system,” said Theodore Strange, MD, associate chair of medicine at Staten Island University Hospital in New York. “So when we give vaccinations, and somebody has a preexisting viral episode with the virus, the body makes antibodies so that if the virus were to appear again, you would fight it.

“The virus is somehow smart enough to know that so that it changes its coding a little bit so that the body can’t detect it,” he explained.

Asked about the odds we’ll see a new COVID-19 variant that current vaccines won’t protect against, Michael Grosso, MD, chief medical officer and chair, pediatrics at Northwell Health’s Huntington Hospital in New York, said it’s just a matter of time.

“There is no question that the longer this virus circulates, the greater the odds that mutations will emerge which protect it from the vaccines we have now,” he said.

However, according to Grosso, we can prevent this by getting vaccinated and stopping the spread of the virus.

“It sounds simplistic, he said. “But the best way to beat the virus is to beat the virus.”

He said the universal implementation of a few rules, such as social distancing, mask-wearing, and high rates of immunization “would be like throwing a bucket of water on a campfire.”

“Controlling the virus and preventing new cases not only help the people who would have become infected,” he continued. “Such steps also prevent the chain of causation, which leads to the emergence of new variants and the relentless cycle of future infection that they could bring.”

He emphasized that the physical, emotional, and economic health of all people hinge on our collective ability to do this.

According to Newman, any circulating variant will pose the risk of more cases, more hospitalizations, and more deaths. Variants can also have the potential to overwhelm health systems and lead to preventable deaths due to a lack of resources such as ICU beds, ventilators, and staff.

“However, it’s important to stay calm,” she said. “The emergence of a new variant doesn’t automatically translate to imminent doom, but we must be vigilant in our infection prevention measures.”

She noted that we’re fortunate to have vaccines largely effective against COVID-19, including the current variants.

Though it’s possible for vaccinated people also to transmit the coronavirus, unvaccinated people are far likelier to develop the disease and have serious symptoms.

Strange said the unvaccinated seems to be the population that’s mostly transmitting the variants.

“I can tell you, on Staten Island we have, of the 44 or so patients in our hospital – 80 percent of them are unvaccinated, and the few that are vaccinated that come in, they’re usually older, sicker, with other medical illnesses,” he said.

“We had a 29-year-old police officer come in. We had a couple of pregnant 23- and 24-year-old women,” he continued. “So, it’s the unvaccinated currently that are the biggest spreader, call them super-spreaders, of this virus in the community.”

Strange emphasized that the only way to decrease the ability of the virus to mutate is not to have a host for it to live in.

“The virus needs a living host. That host happens to be human beings. If we can eliminate that host from getting that virus, usually by vaccination, then we can minimize the whole impact of what mutations will be,” he concluded.

The World Health Organization (WHO) has designated Mu variant COVID-19 a variant of interest, meaning specific genetic markers have developed that could make it more infectious or evade vaccine protection.

Experts say that while new variants can increase the risk of hospitalizations and deaths, we have effective vaccines available. They also say vaccination is the best way to prevent COVID-19 variants because it keeps the virus away from the host it needs to survive – us.