The BA.2 sub-variant of Omicron is 1.5 times more transmissible than the original Omicron strain, according to a study led by Danish researchers. 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 Organization (WHO).
Researchers at Denmark's Statens Serum Institut (SSI) found that BA.2 appeared to be one and a half times more contagious than BA.1, Newsweek reported.
"Of course, we follow the development closely, and if BA.2 is more contagious, it may mean that the wave of infections will be higher and will extend further into February compared to the previous projections," Tyra Grove Krause, an infection epidemiology expert at SSI, was quoted as saying.
The subvariant BA.2, dubbed with the moniker "Stealth Omicron", is rising around the world with at least 55 countries, including India, reporting cases to a global variant tracking database. The database also showed that nearly half of US states have confirmed the presence of BA.2 with at least 127 known cases nationwide as of Friday, CNBC reported.
The Centers for Disease Control and Prevention, in a statement Friday, said although BA.2 has increased in proportion to the original Omicron strain in some countries, it is currently circulating at a low level in the US.
As of January 26, BA.1 was still the most common Omicron sub-variant worldwide, accounting for 98 per cent of cases at that time, the SSI said. But, BA.2 developed quickly and has become Denmark's dominant Covid type.
While there is no evidence that BA.2 is more severe than BA.1, both sub variants have many differences in their mutations. In fact, the difference between BA.1 and BA.2 is greater than the difference between the original "wild strain" and the Alpha variant.
"The BA.2 variant has five unique mutations on a key part of the spike protein the virus uses to attach to human cells and invade them," Troels Lillebaek, the chairman of Denmark's committee that conducts surveillance of Covid variants, told CNBC.
Mutations on this part of the spike, known as the receptor binding domain, are often associated with higher transmissibility. Meanwhile, the UK Health Security Agency said that BA.2 has a "substantial" growth advantage over the original omicron.
However, a preliminary assessment found that BA.2 doesn't appear to reduce the effectiveness of vaccines any more than the original Omicron. A booster dose was 70 per cent effective at preventing symptomatic illness from BA.2 two weeks after receiving the shot, compared with 63 per cent effectiveness for the original omicron strain, the report said.