Dubbed as the “stealth Omicron”, the sub-variant has been classified as a variant under investigation by the UK Health Security Agency on Friday, who said that it could have a growth advantage.

“It is the nature of viruses to evolve and mutate, so it’s to be expected that we will continue to see new variants emerge,” said Dr Meera Chand, incident director at the UKHSA

“Our continued genomic surveillance allows us to detect them and assess whether they are significant,” added Chand.

The sub-lineage was designated in early December last year. 

Detection and sequencing of the variant 

Britain has sequenced 426 cases of the BA.2 sub-lineage. 

Following this, the UKHSA has said that while there was uncertainty around the significance of the changes to the viral genome, the early analysis suggested an increased growth rate compared to the original Omicron lineage, BA.1.

UKHSA said that 40 countries had reported BA.2 sequences, with the most samples reported in Denmark, followed by India, Britain, Sweden and Singapore.

In Denmark, BA.2 has grown rapidly. It accounted for 20% of all Covid cases in the last week of 2021, rising to 45% in the second week of 2022.

Anders Fomsgaard, a researcher at Statens Serum Institut (SSI), said he did not yet have a good explanation for the rapid growth of the sub-lineage, adding he was puzzled, but not worried.

“It may be that it is more resistant to the immunity in the population, which allows it to infect more. We do not know yet,” he told broadcaster TV 2, adding that there was a possibility that people infected with BA.1 might not be immune from then catching BA.2 soon after.

“It is a possibility,” he said. “In that case, we must be prepared for it. And then, in fact, we might see two peaks of this epidemic.”

An initial analysis made by Denmark’s SSI showed no difference in hospitalisations for BA.2 compared to BA.1.   

Why is BA.2 called ‘stealth Omicron’?

The BA.2 does not have the specific mutation seen with Omicron that can help to easily distinguish it from Delta. 

However, many experts have recently claimed that the sub-strain does show up on PCR tests.

“BA.2 _is_ detectable by PCR, these news reports are totally wrong. Depending on the PCR test used it may not look like BA.1 (the other Omicron). But it will still give a positive result. Frustrating to see falsehood about non-detectability still around,” said Cornelius Roemer, a computational biologist at Switzerland’s University of Basel. 

Other sub-strains of Omicron 

According to World Health Organization (WHO), the Omicron variant has three sub-strains – BA.1, BA.2 and BA.3. The Indian SARS-CoV-2 Genomics Consortium (INSACOG) had also earlier informed of the same. 

But now, more sub-variants have been emerging, especially in one of the worst-affected regions of Europe.