‘No cause for alarm’ over Mu variant
Reports point to vaccine resistance, but expert says Delta remains our biggest threat
Even as the Delta variant continues to be the dominant strain of COVID-19 globally, scientists are warning that a new variant dubbed ‘Mu’ — already detected in Ontario — contains a set of mutations indicating it could be resistant to neutralizing antibodies arising from vaccination and infection.
The good news is that the number of global cases of Mu, or B.1.621 as it is officially called, is tiny compared to those of the highly transmissible Delta and has even decreased in some regions in recent months.
But the bad news is that since Mu was first detected in Colombia in January, the variant has spread to 42 countries, including 49 U.S. states.
In Miami, Fla., alone, Mu is responsible for about 10 per cent of all COVID patients, behind Delta.
In Ontario, the variant was first detected on June 23 and has since been found 168 times in the province, mostly in the GTA.
“Any viral variant that is starting to spread is definitely something we should keep an eye on, particularly when we don’t know yet how immune evasive it is,” said Stephanie DeWitteOrr, a virologist and professor in health sciences and biology at Wilfrid Laurier University.
“Right now, Mu is a variant of interest, which means that the mutations that it has qualify to be something we need to look at. The mutations look like something that could either be a more transmissible virus or could be a more immune-evasive virus or a combination of that.”
On Aug. 30, the World Health Organization (WHO) added Mu to its list of variants of interest, which includes four other strains, such as Lambda, first discovered in Peru last December and which has since spread to 29 countries.
The WHO defines variants of interest as those strains with genetic changes that are predicted or known to affect things such as transmissibility, disease severity, and immune escape, and which have caused significant community transmission in multiple countries with increasing prevalence.
Variants of interest are different from the more serious variants of concern, which are characterized by increased transmissibility and virulence, such as Delta and before it, Alpha,
which drove Ontario’s third wave.
WHO experts continue to stress that Delta, which has become the dominant strain of the coronavirus worldwide, remains of primary concern due the fact that it is up to 60 per cent more transmissible than the previously dominant Alpha, and its ability to outcompete other variants. And they point out that, so far, Mu has been unable to transmit to the extent Delta has, even if its genetic makeup suggests that it could be better at evading immunity.
“In some sense, these viruses are competing with each other, not just with us,” Dr. Mike Ryan, executive director of the WHO’s health emergencies program said during a media briefing Tuesday. “Any virus that emerges has got to be able to compete with the ‘best of class’ and at the moment, the best of class in terms of transmission is the Delta variant.
“The Mu variant does contain genotypic sequences and structure that would indicate that it could be better at vaccine escape or other things, but that won’t matter if it can’t transmit efficiently.”
Mutations are essentially random mistakes that are created when a virus makes copies of itself. Many mutations are known as “loss-of-function” mutations which result in the virus becoming less effective or productive or even dying off. But occasionally “gain-of-function” mutations will occur which make the virus more resilient, virulent and transmissible.
“That’s just how viruses work,” explained DeWitte-Orr. “The loss-of-function mutations disappear and the gain-offunction mutations, they’re going to beat out anything before it.”
In its weekly epidemiological update on Aug. 31, the WHO noted that the global prevalence of Mu among sequenced cases is currently below 0.1 per cent, “the prevalence in Colombia (39 per cent) and Ecuador (13 per cent) has consistently increased.”
The agency said further studies are needed to understand Mu’s characteristics and it will continue to monitor the trajectory of the variant in South America, as well has how Mu interacts with Delta.
Back home in Canada, 196 cases of Mu have been detected nationally to date, according to the Public Health Agency of Canada, with the vast majority in Ontario. The agency says most were from July and that over the past few weeks, “cases of the B.1.621 lineage have been decreasing in Canada.”
Public Health Ontario reports that as of Aug. 14, most cases of Mu have been detected in Peel (29), York (24), Toronto (20), Hamilton (15) and Halton (10).
As of now, “there’s certainly no cause for alarm,” said Arinjay Banerjee, a virologist at the University of Saskatchewan who has been studying coronaviruses for eight years. He noted that while some emerging research suggests the Mu variant is more resistant to being neutralized by antibodies, on the whole the antibodies still work.
“The data shows that if you’re vaccinated, you will be protected,” Banerjee said. “If the virus is less neutralized, that doesn’t mean that vaccinated individuals would be severely sick with COVID-19.”
A pre-print study published this week by a team of Japanese researchers found that the Mu variant is “highly resistant” to blood serum collected from vaccinated individuals and people who had recovered from COVID-19. The study, which has not yet been peer-reviewed, also found that Mu was “significantly more resistant” to serum from people who had recovered from COVID-19 than the Beta (B.1.351), which up until now was thought to be the most resistant variant.
“Since breakthrough infection by newly emerging variants is a major concern during the current COVID-19 pandemic, we believe that our findings are of significant public health interest,” the authors note.
Mu has not gone unnoticed by vaccine manufacturers either. In an email to the Star, Christina Antoniou, director of corporate affairs for Pfizer Canada, said the company is currently evaluating its COVID vaccine effectiveness against Mu in a laboratory study and expects to share its findings soon.
She said Pfizer and BioNTech are confident in the protection and safety of the two-dose vaccine, which “continues to be highly efficacious in preventing COVID-19, including variants and to date, no variant, including Delta, appears to have escaped the protection of the vaccine.”
Bottom line, it is still early days for the Mu variant and we don’t yet know if it has the staying power of Delta, says DeWitte-Orr.
“Some variants will arise and they won’t take hold. It’s a numbers game,” she said. “The Mu variant has sequence changes that make it look like it could be a problem. It’s different enough that we have to watch it.”