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- Scientists are closely monitoring the variant of the Mu coronavirus.
- Mu has the potential to resist protection from vaccines or previous infection.
- But Mu isn’t becoming more prevalent – a sign it’s less of a concern than Delta.
Last month, seven fully vaccinated elderly residents of a retirement home in Belgium died from COVID-19. They had all been infected with a variant of the coronavirus now known as Mu.
The outbreak raised questions about whether Mu posed a greater threat than other variants, including Delta. But so far this has not proven to be the case.
Mu carries mutations that could help it bypass vaccine protection – but it is becoming less common over time compared to other variants. This is an indication that Mu will not become dominant, as variants with a big advantage over Delta would quickly represent more cases.
Globally, Mu infections appear to have peaked in mid-July, when they accounted for 0.6% of new coronavirus infections. Today, they represent just 0.1% of new infections worldwide, according to data from GISAID, a database that collects the genomes of coronaviruses.
Mu is spreading across the world, but it’s still rare
Of the 48 countries that have recorded Mu infections this year, only 10 have detected Mu cases in the past month.
The variant is most prevalent in Colombia, which recorded the world’s first Mu cases in January. Mu now accounts for almost all of the new coronavirus infections sequenced there over the past month, according to GISAID.
The United States, Mexico and a handful of European countries – Belgium, France, the Netherlands, Spain and the United Kingdom – have also recorded cases of Mu in the past four weeks.
School employees check the temperature of students at Los Pinares private school in Medellin, Colombia on February 10, 2021.
Joaquin Sarmiento / AFP / Getty Images
But just because a variant is geographically dispersed does not mean that it spreads widely across the world. In the United States, for example, Mu has been detected in almost every state, but the variant accounts for less than 0.2% of new coronavirus infections sequenced over the past month.
“We are monitoring this very closely,” said Dr Anthony Fauci, President Joe Biden’s senior medical adviser, in a briefing last week, adding: “We do not see this as an immediate threat at this time. “
Mu does not appear to be as transmissible as Delta
The World Health Organization called Mu a “variant of interest” in late August. The term applies to variants that can cause extensive community transmission or have genetic changes that could alter the behavior of the virus. At the time, WHO scientists were concerned that Mu had been spreading rapidly in South America since May.
But the prevalence of Mu in South America has fallen since then. At its peak in mid-July, the variant accounted for around 5% of new coronavirus infections in South America. Today, it represents around 3%.
In a study awaiting peer review, Colombian researchers estimated that Mu is 1.2 times more transmissible than the original version of the virus. This gives Delta the edge, as the variant is likely more than twice as transmissible as the original strain.
Still, scientists are watching Mu closely because of its potential to resist the body’s immune defenses.
Scientists most concerned about Mu’s resistance to vaccine protection
Maria van Kerkhove, WHO technical officer on COVID-19, told The Associated Press that the variant “interests us because of the combination of mutations it has.”
Mu carries several key mutations in the spike protein’s genetic code – the crown-shaped bumps on the surface of the virus that help it invade our cells. These mutations could make it resistant to antibodies produced by vaccines or a previous infection, which target the spike protein to neutralize the virus.
A health worker prepares a syringe before applying it to the patient during a vaccination exercise in Bogota, Colombia, in January 2021.
Guillermo Legaria / Getty Images
A study suggested last month that the presence of these mutations may justify the reclassification of Mu as “a variant of concern” – a term reserved for a handful of the most disturbing variants to date, including Delta. Another study, which has not yet been peer-reviewed, found that Mu is more resistant to neutralizing antibodies from Pfizer’s vaccine or to a previous infection than any other variant of concern.
Italian researchers, however, have found evidence that Pfizer’s vaccine still neutralizes the Mu variant, even though the vaccine offers better protection against the original version of the virus. Their study concluded that Mu is “not of concern for the effectiveness of the vaccine”.
Many scientists expect variants like Mu to continue to emerge, given the extent to which the virus has spread.
“The virus itself is always changing phenotype and probably becoming more infectious and adapting to drug treatment regimens,” Andrew Read, a professor at Pennsylvania State University who studies the evolution of infectious diseases told Insider last month. . “There’s no reason to think it’s going to take hold in the short term. What we hope is that it will come close to peak infectivity in the short term.”
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