The World Health Organisation (WHO) is monitoring the new COVID-19 strain 'Mu' which was recently designated as a variant of interest (VOI) for vaccine resistance, the health body has said.

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Mu, also known as B.1.621, was first identified from Colombia in January this year. Infections from Mu have since been recorded in South America and Europe. Based on the latest round of assessments, B.1.621 was classified as a VOI on 30 August 2021 and given the WHO label 'Mu'.

Mu variant has various mutations which indicate that it could be more resistant to vaccines, similar to the Beta variant, the WHO said in its weekly epidemiological update on 1st September. "The Mu variant has a constellation of mutations that indicate potential properties of immune escape. Preliminary data presented to the Virus Evolution Working Group show a reduction in neutralisation capacity of convalescent and vaccine sera similar to that seen for the Beta variant, but this needs to be confirmed by further studies," the UN health agency said.

As of August 29, over 4,500 sequences (3,794 sequences of B.1.621 and 856 sequences of B.1.621.1) have been uploaded to the open-access database GISAID (Global Initiative on Sharing Avian Influenza Data) from 39 countries.

While the global prevalence of the Mu variant among sequenced cases has declined and is currently below 0.1 per cent, the prevalence in Colombia (39 per cent) and Ecuador (13 per cent) has consistently increased, the WHO said. "The epidemiology of the Mu variant in South America, particularly with the co-circulation of the Delta variant, will be monitored for changes," the health agency added.

There are four coronavirus variants of concern, as deemed by the WHO, with the Alpha variant -- first recorded in Kent, England -- seen in 193 countries, Beta in 141, Gamma in 91 and Delta in 170 countries, while Mu is the fifth variant of interest.