COVID variant Mu added to WHO interest list, may reduce vaccine effectiveness

A new COVID strain has been added to the World Health Organisation’s watchlist that may be more resistant than previous strains to vaccines.

The Mu variant of COVID-19, also known as B.1.621, was first detected in Colombia in January and has now been identified in at least 39 countries.

A study published in the Lancet Infectious Diseases on August 13 found "two cases of a potential vaccine-escape".

It was found to contain spike mutations that show "reduced neutralisation by antibodies".

It also found the variant harbours a spike mutation that was associated in Beta, a previous variant, with a weakened vaccine response.

The Mu variant is the first to be added to the WHO's “variant of interest” watchlist since the Lambda variant (C.37) on June 14.

It has a "constellation of mutations that indicate potential properties of immune escape," the WHO's weekly bulletin said.

The Mu variant carries the mutation D614G, also found in the Delta variant. Research by the Scripps Research Institute in the US found Mu “may increase infectivity”.

Worldwide, the proportion of COVID cases with the Mu variant is below 0.1 per cent. However, it has “consistently increased” in Colombia, where it is now at 39 per cent and 13 per cent in Ecuador, a WHO spokesperson 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.

"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's variant of interest means the strain has:

• Genetic changes that are predicted or known to affect virus characteristics such as transmissibility, disease severity, immune escape diagnostic or therapeutic escape.

• Cause significant community transmission or multiple COVID-19 clusters in multiple countries, in multiple countries with increasing relative prevalence alongside an increasing number of cases over time.

• Other apparent epidemiological impacts that suggest an emerging risk to global public health

There are currently four variants of concern: Alpha, Beta, Gamma and Delta and five variants of interest: Eta, Iota, Kappa, Lambda, Mu, are to be closely monitored.