What we know about the Omicron sub-variant BA.2

A new version of the highly transmissible Omicron variant of the coronavirus has generated a fresh debate owing to its rapid spread in some countries, as scientists keep a close watch to understand if the sub-variant — known as BA.2 — will influence the course of the pandemic.

Data is scarce at this point. But there are indications that BA.2 is not more virulent than the original Omicron variant, prompting experts to caution against sounding the alarm. However, some suggest that this sub-variant could be more transmissible.

As the debate grows, it is the lack of data that has triggered a series of questions over its response to vaccines and ability to cause re-infections, among others.

What we know so far

BA.2 is not a new variant. It is a sub-variant — like BA.1, which is responsible for the new waves of infections around the world this winter. Both of them are recognised as the Omicron variant (along with BA.3).

While BA.1 and BA.2 have several mutations in common, they are some 20 mutations apart, according to experts. BA.2 has some genetic traits that make it indistinguishable from other variants in certain PCR tests. This is where it differs from BA.1. And because of this, BA.2 has been termed the "stealth variant" — meaning it's harder to detect.

But that doesn't mean BA.2 evades laboratory tests. A PCR test still detects the coronavirus in case of a BA.2 infection, though the time-consuming genome sequencing process is necessary to identify the sub-variant.

According to reports, BA.2 has been found in over 40 countries, including the United States, the United Kingdom, Denmark and India. While authorities in the UK has designated BA.2 as a variant under investigation, the World Heath Organization (WHO) has called for investigations into its characteristics.

READ MORE: WHO: Omicron may infect over half of Europe in two months

A debate begins

Consistent growth across multiple countries suggests that BA.2 could be more transmissible than BA.1, according to Tom Peacock, a virologist at the department of infectious diseases at London's Imperial College.

"...this is really where the evidence mostly ends - we do not currently have a strong handle on antigenicity, severity or a much evidence for how much more transmissibility BA.2 might have over BA.1 - however we can make some guesses/early observations," he continues in a Twitter thread.

He points out that "the coming weeks should make everything a lot clearer".

Apart from the transmission factor, two other questions that weigh heavily on experts' minds are whether a person who contracted the original Omicron variant recently can be re-infected by BA.2, and how the sub-variant would react vis-à-vis vaccines.

"...there is likely to be minimal differences in vaccine effectiveness against BA.1 and BA.2 and, it's also highly likely BA.1 infection will give decent cross-reactivity against BA.2 infection," Peacock says on Twitter.

In Denmark, BA.2 is believed to have outpaced BA.1, accounting for about 65% of the new infections in the country. This has prompted some experts to argue that BA.2 could have some "competitive advantage".

But experts and authorities reiterate there is no indication that BA.2 causes more severe infections. In fact, according to reports, ICU admissions are coming down in Denmark despite the surge in BA.2 cases.

"There is no evidence that the BA.2 variant causes more disease, but it must be more contagious," Danish Health Minister Magnus Heunicke told a news conference on Wednesday.

Preliminary calculations suggest BA.2 could be 1.5 times more infectious than BA.1, Denmark's top infectious disease authority, Statens Serum Institut (SSI), has said in a note, according to news agency Reuters.

But an initial analysis by the institute showed no difference in the risk of hospitalisation.

“There is no evidence so far that BA.1 and BA.2 are different in respect of immune escape, virulence or the age profile they preferentially infect. At this stage, BA.1 and BA.2 can be considered as two epidemiologically largely equivalent sub-lineages of Omicron," says Francois Balloux, Professor of Computational Systems Biology and Director of UCL Genetics Institute in London.

“Based on all the current evidence available, changes in the relative frequency of the BA.1 and BA.2 Omicron sub-lineages do not warrant the imposition of any pandemic restriction or the lifting of existing ones," Balloux adds in comments to Science Media Centre.

READ MORE: Did Omicron originate in mice before jumping to humans?