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.