Scientists are closely watching an Omicron subtype spreading in Denmark, the UK, Singapore and India

• Scientists worldwide are closely tracking an Omicron subtype, called BA.2.
• In Denmark BA.2 is surpassing the BA.1 Omicron subtype, the most common cause of new COVID-19 cases.

Health officials and scientists worldwide are closely watching a subtype of the highly infectious Omicron COVID-19 variant.

The new subtype, called BA.2, is a sister to BA.1 — the virus driving most COVID-19 cases worldwide.

Scientists have spotted that the number of people infected with BA.2 has steadily increased in several countries including India, the UK, Sweden, and Singapore. It was first detected in the Philippines in December 2021.

This could signal BA.2 is more infectious than BA.1, though there isn't enough data yet to determine any meaningful difference between the two, experts have said.

Scientists worldwide are now scrambling to work out if current vaccines will still work on the subtype, and whether BA.2 is more deadly.

In Denmark, BA.2 has displaced BA.1 and now accounts for almost half of the new infections in the country, health officials said Thursday. Early data from the country suggests there hasn't been an uptick in hospitalizations since the subtype took hold.

Dr Tom Peacock, a researcher at Imperial College London, who was one of the first to sound the alarm about Omicron in November, said on Twitter Friday that BA.2 probably wouldn't cause a a second Omicron wave: "I think the likely scenario is BA.2 just exacerbates what the national Omicron situation is (slows down decreases, increases peaks, etc)."

Peacock said that the subtype was not a "major cause of concern", but "definitely worth keeping an eye on," per the Financial Times.

Omicron comprises three viruses: BA.1, BA.2 and BA.3.

The BA.1. and BA.2 sister viruses share common mutations, but there are about 50 that differ between either subtype, Peacock said Sunday.

Francois Balloux, director at the University College London Genetics Institute said in a statement to the Science Media Center Monday that the two Omicron sub-lineages were sisters that split from each other several months ago, and were not derived from each other.

Scientists have previously warned that BA.2. is a bit harder to track in lab tests than BA.1 due to mutations in the part of the virus that attaches to cells.

As of Monday, the BA.2 Omicron subtype had been detected in 10,811 sequenced tests from 49 countries and 17 US states, according to Scripps University's Outbreak.info. Outbreak.info pulls data from a well-regarded central database called the Global Initiative on Sharing Avian Influenza Data, or GISAID.

Countries with more than 100 BA.2 cases include: Denmark (8,357), India (711), the UK (607), Sweden (224), and Singapore (203). But as a percentage of cases overall, it remains low. For example, BA.2 accounts for about 0.03% of all tests sequenced in the UK, according to Outbreak info.

UK health officials labeled BA.2 a "variant under investigation" on Friday. This essentially means UK officials are concerned about its mutations, but it hasn't yet been determined whether the subtype is more deadly, more infectious or better able to evade vaccines.

The UK Health and Security Agency said Friday that their decision was based on "small but increasing numbers" of the virus in the country and its spread internationally. "There is still uncertainty around the significance of the changes to the viral genome, and further analyses will now be undertaken," it 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, UKHSA COVID-19 incident director, said.