Delta sub-lineage, AY.25

"It's hard to say what the ceiling is. It will keep climbing to find a peak of adaptation. But we don't really know how close to the peak we are."

"If the infections are more severe, if they're more likely to be causing breakthrough infections, we have no idea."

"[Were outbreaks targeted for the] jackpot [effect]? Where cases happened to be growing, particularly in the western provinces, and this was the lucky virus that happened to be at the right place at the right time?" 

"When you see it in separate jurisdictions, it does become increasing evidence that there is a real transmission advantage [that the AY.25 sub-strain is more infectious than the Delta original]."

"It's more or less what we would expect in a growing viral population, as was the case in the reopening, particularly in the western provinces this summer."

Jesse Shapiro, associate professor, department of microbiology and immunology, McGill University, Montreal

"The trunk [of the virus 'tree'] is close to Wuhan 1, because that's the earliest sequence we have. [A] variant of concern [like Delta and Alpha are like heavy branches]."

"We have a way of talking about specific parts of that tree. Especially when parts of the tree carry mutations of public health significance."

"But the virus is going to evolve as long as it can infect people. And the best way that we can reduce the number of infections is to have as many Canadians vaccinated as possible."

Art Poon, associate professor in virus evolution, Western University

Students, most of them wearing masks, leave William Aberhart High School at the end of the day in northwest Calgary on Oct. 5, 2021. Photo by Jim Wells/Postmedia

 

The threatening new virus villain is yet another offshoot of the offshoot/variant of the original SARS-CoV-2 virus causing COVID-19, which first appeared in Wuhan, China, and once again the newest mutation strain is more virulently contagious than its predecessors. Several Delta descendants are now in circulation in Canada, and to all appearances they have a survival advantage over the parent strain. And as long as the virus itself in its variant forms remains in circulation, the greater the opportunities for it to continue mutating.

Scientists have identified two sub-lineages, identified as AY.25 and AY.27. Detected in the spring in Canada, where cases have been popping up in every province barring Prince Edward Island. Western Canada has hosted the highest numbers of these AY.25 infections in the process to becoming the predominant strain circulating in Saskatchewan, struggling with its latest still-rising wave. Of 1,670 cases confirmed in Ontario, AY.25 has been sequenced in the most recent four-week reporting period.

Over 38,000 sequences right across Canada have been filed to a global data portal meant to track the spread of SARS-CoV-2 variants. Canada's COVID variants rapid response network alongside reports from provincial and federal labs will be publishing a detailed report shortly. While the new variants are steadily increasing in frequency it remains unclear how the biology of COVID-19 is impacted. India was first to identify the sub-lineages which appear to be endowed with an advantage to the extent that modelling identifies their spread and growth; up to five percent faster.

Delta, in its initial manifestation, had a transmission advantage over Alpha of between 40 to 60 percent in comparison. Yet each leap in transmisibility advantages the virus, variant by variant. The variants, mutating from the original Wuhan strain have accelerated the spread of the virus on a worldwide basis while having the potential to spread or cause increasing cases of severe outcomes. AY.27 has seen the spike protein enabling the virus to enter human cells more readily.

 

Another variant titled AY.4.2 has been described as "Delta plus" and that speaks volumes about its potential which is currently bedeviling the United Kingdom. On the plus side, no evidence has yet been detected of any of the mutants exhibiting immune escape; that they have adapted to evade vaccine efficacy. "But it tells us this virus still seems to have plenty of room for adaptation", explained Dr. Poon.

 

The sub-lineages have been active in Canada for months, April at the earliest, "but through everyone's contributions, by being vaccinated and wearing your mask indoors and so on, we have still seen [COVID-29] cases go slow [in most parts of the country". The implication being that should they ultimately present as the dominant strain nationally, "that there's not going to be a sudden transition, and everything  radically changes". 

A 3d representation of the Delta variant.

In the final analysis the virus retains the capability of evolving to the extent of the number of people the virus can infect. Viral evolution does not necessarily occur exclusively in the fully unvaccinated, but the opportunity for new strains to evolve remains, as long as there are people vulnerable to infection, and those most vulnerable are the unvaccinated.

"[The larger the number of unvaccinated, the greater the potential] for new mutants, new variants and the replication of those variants across the population."

"There is a clear concern about people who are choosing not to be vaccinated."

Catalina Lopez-Correa, executive director, Canadian COVID Genomics Network