The WHO and the Centers for Disease Control and Prevention (CDC) have three categories of COVID-19 variants: variants of interest (VOI), variants of concern—which includes Alpha, Beta, Delta and Gamma—and variants of high consequence.
The WHO officially labeled the Mu variant a VOI on August 30, which indicates the variant has genetic differences to the other known variants and is causing infections in multiple countries, and it may present a particular threat to public health. However, the numbers globally are low at present, so it is not currently a variant of concern.
When Professor Anna Durbin, Director, Center for Immunization Research, Johns Hopkins Bloomberg School of Public Health, was asked if Mu had been out-dominated by Delta, she replied “this is most likely explanation.”
“Virus strains are competing with one another and it is definitely survival of the fittest, essentially the virus that can infect more people faster. It is likely that Mu was not able to out-compete delta,” she added. “I also think vaccines contributed, as they provide protection to more people making fewer susceptible hosts. “The more viruses replicate, the more they are able to mutate and adapt. Vaccines provide protection and reduce the amount of infectious virus and reduce the amount of time viruses can replicate. This means the virus has much less opportunity to mutate and adapt.”
Researchers in Japan released a study on Monday showing that the Pfizer-BioNTech COVID-19 vaccine seems to be adequately effective against the B.1.621 (Mu) variant.
A team of scientists from Yokohama City University School of Medicine and Yokohama City University Hospital found that the vaccine is 76 percent effective in neutralising the variant. A dual monoclonal antibody cocktail containing casirivimab and imdevimab was also found to be effective.
Delta variant remains the dominant strain in the U.S., accounting for nearly 100 percent of all sequenced samples. However, cases have been declining for several days, suggesting the country might have seen the peak of the summer wave of the variant. But the projection for the winter months remains uncertain. According to data from the CDC, the country’s seven-day moving average of cases has been declining since September 14, when the daily average of new cases was just under 150,000. The daily average was 95,228 for September 26.