The World Health Organization said it is monitoring another new COVID-19 variant with mutations that the agency fears could make it resistant to vaccines.

The Mu variant, also known as B.1.621, was added as a "variant of interest" to the organization’s watchlist Monday.

"The Mu variant has a constellation of mutations that indicate potential properties of immune escape," the bulletin said.

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Preliminary data indicated that it may evade vaccines in a way similar to the Beta variant, but experts said more research on the strain is necessary.

Since first emerging in Colombia in January 2021, the Mu variant has popped up in at least 39 countries.

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"Although the global prevalence of the Mu variant among sequenced cases has declined and is currently below 0.1%, the prevalence in Colombia (39%) and Ecuador (13%) has consistently increased," the agency said, though it added the uptick could be due to increased genetic sequencing.

The concerns over the new strain come as the highly contagious Delta variant has driven surges in cases across the globe.