The World Health Organization is warning of a newly named COVID-19 variant that could potentially have resistance to the vaccines.
The Mu variant— which also has the scientific name B.1.621 — was first detected in Colombia in January.
Over 4,600 cases have been spotted since then, and it has spread to more than 40 countries.
Almost 2,000 cases of the variant have been detected in the United States.
The WHO's weekly bulletin claimed its mutations suggest it may be more resistant to vaccines, as was the case with the South African 'Beta' variant.
There are fears it may be more infectious, too.
But the agency warned more studies would be needed to examine this further, with the WHO having now formally labelled Mu a 'variant of interest'.
Almost 4,000 cases of the variant have been detected to date since it first emerged in January, but the number of infections has fallen in recent weeks, coinciding with the rapid increase of the Delta variant. This graph shows the seven-day average proportion of cases that were due to the Mu variant worldwide. They reveal its prevalence has fallen recently
The variant was first spotted in Colombia in January. It has since been detected in 40 countries
In the US it made up almost one per cent of infections in July but the number of infections then declined in August amid the spread of the Delta variant
In Colombia — where it was first identified — it is still behind around six in ten cases. But the proportion of cases it makes up in the country has also begun to fall
The WHO report said: '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.
'Although the global prevalence of the Mu variant among sequenced cases has declined and is currently below 0.1 percent, the prevalence in Colombia (39 percent) and Ecuador (13 percent) has consistently increased.
'The epidemiology of the Mu variant in South America, particularly with the co-circulation of the Delta variant, will be monitored for changes.'
The WHO currently lists four Covid variants of concern — Alpha, Beta, Gamma and the highly-transmissible Delta.
