Even as Omicron has been showing signs of peaking, some European countries are seeing the rise of Omicron subvariant BA.2, sparking concern among the scientific community.

The subvariant BA.2, dubbed with the moniker "Stealth Omicron," appears to be gaining ground in certain parts of the world, including Denmark and the UK, Euronews reported. It is rapidly outpacing other Omicron subvariants, and sparking fears that a more transmissible strain of COVID is actively spreading through the community.

The UK Health Security Agency, recently, designated the BA.2 as a variant under investigation. "53 sequences of the BA.2 sub-lineage of Omicron had been identified in the United Kingdom," it said in a statement. "This sub-lineage, which was designated by Pangolin on December 6, does not have the spike gene deletion at 69-70 that causes S-gene target failure (SGTF), which has previously been used as a proxy to detect cases of Omicron. 'UKHSA is continuing to monitor data on the BA.2 sub-lineage closely," the statement said.

"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 as the pandemic goes on," Dr Meera Chand, Incident Director of the UKHSA, was quoted as saying. "Our continued genomic surveillance allows us to detect them and assess whether they are significant," she added.

Omicron, which is also referred to as B.1.1.529, has three main substrains, BA.1, BA.2, and BA.3, according to the World Health Organisation (WHO). Up until now, it has been BA.1 that has been dominating with the WHO estimating it makes up a large majority of all Omicron cases. However, in some places, the BA.2 has begun to spread faster, the report said.

In Denmark, it now makes up almost half of all Omicron cases. Other countries such as Norway and Sweden are also experiencing an increase in BA.2 cases, although not to the same extent. "Initial analysis shows no differences in hospitalisations for BA.2 compared to BA.1," said Denmark's Statens Serum Institut, a government-run infectious disease research centre, in a statement. "Analyses regarding infectiousness and vaccine efficiency etc. are ongoing, including attempts to cultivate BA.2 in order to perform antibody neutralisation studies." The institute stated that vaccines likely have an effect against severe illness from BA.2 infection.