Mu COVID Variant Could Potentially Escape Immunity But Delta is Still “Most Concerning”, WHO Says

While COVID-19 cases caused by the Delta variant continue to wreak havoc, last week, the World Health Organization added a new variant called Mu (B.1.621) to its list of Variants of Interest. The Mu variant harbors several mutations in the spike protein-coding genes that could help it evade immunity arising from natural infection or vaccination.

“The Mu variant has a constellation of mutations that indicate potential properties of immune escape,” the WHO said in its report last week.

Global Infection Status of the Mu Variant

The Mu variant, which was first detected in Colombia in January, has spread to 43 countries so far, with at least 4,700 cases identified worldwide via genomic sequencing. Although the global prevalence rate of the variant is less than 0.1%, its prevalence has “steadily increased” in Colombia and Ecuador, where it now accounts for about 39% and 13% of infections, respectively.

In addition to South America, cases of the Mu variant have also been reported in the US, Europe, and Asia. The Mu variant has now spread to 49 US states (except Nebraska) with over 2,000 confirmed cases as per recent reports. Among them, California has recorded 384 Mu variant cases, with 167 cases contained in Los Angeles County area. In addition, Florida, which has recorded the most new COVID-19 deaths, has also detected several Mu variant cases.

More than 50 cases have been detected in the UK, with one case identified in Wales. A limited number of cases have also been confirmed in Asia, with Hong Kong, China, Israel, Japan, Taiwan, and South Korea reporting recently.

How Different is the Mu Variant?

The Mu variant has the P681H mutation originally identified in the alpha (B.1.1.7) variant. P681H is associated with increased transmissibility and is one of the three mutations hypothesized to have the largest potential biological effect.

However, the biggest concern is whether the COVID-19 vaccines designed against the original strain can protect the vaccinated individuals. This is because the Mu variant also carries E484K and K417N mutations associated with immune escape. These are the same mutations found in the beta (B.1.351) variant against which some vaccines offer poor protection.

According to a recent study published in the Journal of Medical Virology, vaccination with Pfizer/BioNTech mRNA vaccine can produce robust protection against the Mu variant. However, compared to other variants, the protection is still low. Nevertheless, further research is required to confirm whether the Mu variant can evade immunity arising from natural infection or vaccination.

Delta Still Remains “Most Concerning”

While the Mu variant is hogging the headlines, the WHO stated that the Delta variant is still the fast-spreading coronavirus that is “most concerning.”

“I think the Delta variant for me is the one that’s most concerning because of the increased transmissibility,” said Dr. Maria Van Kerkhove, the agency’s Technical Lead for COVID-19. “It’s doubly transmissible compared to the ancestral strain, which means that it can spread to more people.”

She added that while the proportion of Mu cases in South America is increasing, the numbers are decreasing in other countries where the Delta variant is prevalent.

Talking about similar Delta-like variants, Dr. Mike Ryan, Head of the Health Emergencies Program at WHO, said, “We will expect to see more. Not every variant means the sky is going to fall in. Each variant needs to be looked at for its characteristics in terms of its potential to cause more severe disease, its potential to transmit, its potential to escape vaccines.”

Author

Rajaneesh K. Gopinath