The mu coronavirus variant has been marked as a “variant of interest” by the World Health Organization and has spread across Chile, Peru and parts of the U.S. and Europe.

Mu variant is the fifth coronavirus variant of interest being monitored by the organization. Stuart Ray, a professor of medicine at John Hopkins University, said the variant accounts for most cases in Colombia, Chile and Peru but only some cases in the U.S.

In the U.S., the variant accounts for about 2,000 cases as of Friday, according to the Global Initiative on Sharing All Influenza Data. The states with the highest mu variant cases are California, Florida, Texas and New York.

The mu variant was first detected in January 2021 in Colombia and has since spread to parts of South Korea, Canada, Europe and Japan, according to WHO.

As of now, Ray said, what’s concerning is mu has similarities to deadlier variants such as the delta variant, which is the cause of more than 99% of cases in the U.S.

Top infectious disease expert Anthony Fauci said at a news briefing Thursday that the government was “keeping a very close eye on it.” But he confirmed that the dominant and most concerning coronavirus variant remains the delta strand.

Ray said it’s highly unlikely the mu variant and other variants would surpass the delta variant cases.

“It’s still early and difficult to measure how infectious and how effective the mu variant is. But the world is a small place during the pandemic, so we’re staying vigilant,” Ray told USA TODAY.

In Colombia and Peru, Ray said, the variant has shown “high rates of transmissibility,” but there’s no reason for concern in the U.S. yet.

Until more cases or research on the mu variant is released, Ray urged Americans to continue to wear masks and get vaccinated.

“Certain features in coronavirus variants appear to make the virus more infectious, and we are seeing some of those features in the mu variant,” Ray said. “But right now, we don’t have any huge concerns.”