The World Health Organization has said it is monitoring a new coronavirus variant known as "Mu", which was first identified in Colombia in January.

Mu, known scientifically as B.1.621, has been classified as a "variant of interest", the global health body said Tuesday in its weekly pandemic bulletin.

The WHO said the variant has mutations that indicate a risk of resistance to vaccines and stressed that further studies were needed to better understand it.

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

There is widespread concern over the emergence of new virus mutations as infection rates are ticking up globally again, with the highly transmissible Delta variant taking hold -- especially among the unvaccinated -- and in regions where anti-virus measures have been relaxed.

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All viruses, including SARS-CoV-2 that causes Covid-19, mutate over time and most mutations have little or no effect on the properties of the virus.

But certain mutations can impact the properties of a virus and influence how easily it spreads, the severity of the disease it causes, and its resistance to vaccines, drugs and other countermeasures.

The WHO currently identifies four Covid-19 variants of concern, including Alpha, which is present in 193 countries, and Delta, present in 170 countries.

Five variants, including Mu, are to be monitored.

After being detected in Colombia, Mu has since been reported in other South American countries and in Europe.

The WHO said its global prevalence has declined to below 0.1 percent among sequenced cases. In Colombia, however, it is at 39 percent.