In its weekly epidemiological update, published on Tuesday, WHO warned it was becoming increasingly prevalent in Colombia and Ecuador, and showed signs of possible resistance to vaccines.

Mu was first identified in Colombia in January 2021, and since then, there have been “sporadic reports” of cases and outbreaks in South America and Europe, WHO said.

While the global prevalence of Mu among sequenced COVID-19 cases is below 0.1%, its prevalence has “consistently increased” in Colombia and Ecuador, where it is now responsible for around 39% and 13% of infections, respectively.

Reports on the variant’s prevalence should be “interpreted with due consideration” given the low sequencing capacity of most countries, the agency said. 

More resistant to vaccines

Mu is the fifth variant of interest to be monitored by the WHO since March. It has a number of mutations that suggest it could be more resistant to vaccines, the health agency warned, but stressed that further research would be needed to confirm this.

Preliminary data show a reduced effectiveness of vaccines “similar to that seen for the Beta variant”. The WHO said it would be monitoring “the epidemiology of the Mu variant in South America, particularly with the co-circulation of the Delta variant…for changes”

More infections

As of 29 August, over 4,500 sequences (3,794 B.1.621 sequences and 856 B.1.621.1 sequences), genome sequences, analysed samples of the virus taken from patients, have been designated as Mu in the past four weeks. The sequences are used to track how it moves through the population, on an open-source genome repository, known as GISAID.

Most of these have been reported in the U.S (2,065) and Colombia (852), Mexico (357) and Spain (473). 

Although this figure will be affected by both sequencing capacity, surveillance and the total number of cases in an area.

The novel coronavirus pandemic has killed at least 124,811 people in Colombia, according to a WHO report on Wednesday.

More than 4,905,258 confirmed cases have been officially diagnosed across the country since the start of the epidemic. As of August 27, a total of 34,247,170 doses of vaccine had been administered.

C.1.2, not currently a concern

South African scientists are closely monitoring the development of another new variant there, according to news reports in the country.

However, C.1.2, is not yet a variant to follow, nor a variant of concern, according to the classification of the World Health Organization.

"It does not appear that its circulation is increasing”, said Dr. Margaret Harris, a spokesperson for the WHO, during a UN press briefing in Geneva on Tuesday.