New Covid-19 MU variant, also known as B.1.621, could be more vaccine-resistant and being closely monitored by the World Health Organization (WHO).

In its weekly epidemiological update, issued on Tuesday, WHO warned that this variant was growing more common in Colombia and Ecuador, and that there were signs of probable vaccination resistance.

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

Mu variant has “consistently increased” in Colombia and Ecuador, where it currently accounts 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 already spreading in the U.S. and has been here for over a month.

What do we know about Mu variant?

Covid MU variant is more resistant to vaccines

Mu variant is the fifth variant of interest to be monitored by the WHO since March.

WHO says Mu has genetic mutations that indicate resistance to natural immunity and the vaccines that have been approved so far.

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”.

MU variant is more infections

In the last four weeks (as of 29 August), over 4,500 sequences (3,794 B.1.621 sequences and 856 B.1.621.1 sequences), genome sequences, and analysed samples of the virus taken from patients have been designated as Mu variant.

The majority of these have been reported in the United States (2,065), Colombia (852), Mexico (357), and Spain (473).

Although this figure is influenced by sequencing capacity, surveillance, and the total number of cases in a given area.

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

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.

Comments by CDC

Mu has also been designated as a variant of interest by the Centers for Disease Control and Prevention. But it has not yet been elevated to the level of variant of concern, which indicates “a significant impact on transmissibility, severity, and/or immunity.”

The European Center for Disease Control and Prevention notes that it could have a significant impact, but warns that data is still preliminary.

C.1.2, not currently a concern

South African scientists are closely monitoring the development of another new variant there. However, C.1.2, is not yet a variant to follow, nor a variant of concern, according to WHO.

“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.

Japan confirms first cases of COVID-19 MU variant

Japan confirmed its first two cases of COVID-19 MU variant during airport screenings in June and July, according to the health ministry.

The MU variant was discovered in a woman in her 40s who arrived from the United Arab Emirates on June 26th, according to the ministry on Wednesday night. Another woman in her fifties who arrived in Japan from the United Kingdom on July 5 also had this variant, according to the report. The two women had no symptoms.

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