A new coronavirus “variant of interest” named Mu – also known by its scientific name as B.1.621 – is being closely monitored by the World Health Organization (WHO), the agency has said. 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. 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” 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).