With signs of the COVID-19 Omicron wave having peaked in parts of the world, including Canada, scientists are keeping a close eye on a subvariant that is rapidly spreading in some countries.
The BA.2 sub-lineage of Omicron, which was first detected in November last year, was designated as a variant under investigation by the U.K. Health Security Agency (UKHSA) on Friday.
More than 10,000 cases have been reported in 47 countries, according to data by cov-lineages.org.
Canada’s chief public health officer Dr. Theresa Tam said Friday more than 100 cases of BA.2 have been detected in the country so far since November. That’s up from the 51 cases the Public Health Agency of Canada (PHAC) confirmed to Global News on Tuesday. PHAC said the cases detected had been mainly from international travellers.
“The virus is multiplying so much now globally that a new variant will pop up, and there are already subvariants related to the Omicron (variant),” said Dr. Horacio Bach, an infectious diseases expert at the University of British Columbia.
The Omicron variant of concern, B.1.1.529, has four sub-lineages: BA.1, BA.1.1, BA.2 and BA.3.
BA.1 accounts for the vast majority of the Omicron cases to date globally, according to the World Health Organization (WHO).
All viruses mutate and have subvariants that have a different genetic makeup than the original variant but have a common origin, said Levon Abrahamyan, a virologist at the University of Montreal.
Here is what we know so far about the BA.2 subvariant.
The BA.2 descendent lineage differs from the original Omicron strain BA.1 in some of the mutations, including in the spike protein, according to the WHO.
The BA.2 lineage has many similarities to BA.1 but does exhibit differences, including in some mutations that may affect transmissibility, detection and possibly immune escape, Anne Genier, a PHAC spokesperson, said.
Early analyses suggest BA.2 has an increased growth rate compared to BA.1, the UKHSA said.
In Denmark, cases of BA.2 are rising rapidly, accounting for nearly half (45 per cent) of all Omicron cases in the country.
Norway, too, has seen a spike from seven detections on Jan. 4 to 611 on Jan. 19.
“This variant of the Omicron virus is growing strongly compared to the original Omicron virus, BA.1,” the Norwegian Institute of Public Health said in its weekly report.
“The properties of the virus are not known other than that it is more contagious than BA.1 and is also increasing in Denmark and Sweden, and may appear to be taking over BA.1 already.”
However, experts say additional research is needed to better understand how much more transmissible this subvariant is than the original Omicron.
“If it is more transmissible, the vulnerable population will be impacted more,” he added.
The WHO said investigations into the characteristics of BA.2, including immune escape properties and virulence, should be prioritized independently to BA.1.
BA.2 has been dubbed the ‘stealth’ Omicron by some scientists because its genetic composition makes its harder to track in a polymerase chain reaction (PCR) test.
The UKHSA said that BA.2 lacks the genetic deletion on the spike protein which produces S-gene target failure (SGTF) in some PCR tests, which has been used as a proxy for Omicron cases previously.
Abrahamyan said it is not uncommon for PCR tests to miss infection or present a false negative, which can be due to the number of domains of the SARS-CoV-2 genome it is trying to detect.
To detect subvariants more efficiently, whole genome sequencing is usually done that can help identify all the mutations of the virus, he said.
Severity of illness and hospitalization
As an increasing number of cases are detected, BA.2 does not appear to cause more severe illness than BA.1.
But data is limited, according to Dr. Meera Chand, COVID-19 Incident Director at UKHSA.
Initial analysis by Denmark’s Statens Serum Instiut shows no differences in hospitalizations for BA.2 compared to BA.1.
“So far, the good news is that it seems that the rate of hospitalization, it doesn’t really differ a lot from the original variant of Omicron,” Abrahamyan said.
Will the vaccines work?
A growing body of research has shown that COVID-19 vaccines are standing up to the Omicron variant, at least among people who received booster shots.
Both Pfizer and Moderna are working to develop booster vaccines that can specifically target the Omicron variant.
Levon said it is most likely that those shots will also be effective against the subvariants.
Denmark’s SSI said analyses regarding vaccine efficiency are ongoing.
“It is expected that vaccines also have an effect against severe illness upon BA.2 infection,” the institute said.
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