Rapid antigen detection: five questions you need to know about Omicron

Omicron Variant BA.2: five questions you need to know

The new coronavirus variant Omicron is highly contagious, and now half of the new coronavirus infections in the world are Omicron.

Omicron is a variant of the new coronavirus, and there are several subtypes of the Omicron variant, the most common one is BA.1.

In many countries, especially in Asia and Europe, there are more and more cases of Omicron BA.2 subtype infection.

So what should we pay attention to for this newly emerging Omicron BA.2 subtype? The BBC has put together five questions you need to know as below.

Why are they called "stealth" mutants?

The Omicron BA.2 subtype is also known as the "stealth variant" because it lacks the genetic signature of the Omicron BA.1 "standard subtype" that allows researchers to determine infection the case is Omicron, not the Delta strain.

Like other mutant strains, people infected with Omicron BA.2 can use antigen testing (quick screening test) or PCR test to determine whether they are positive, but these two tests cannot confirm whether the infection is Delta or Omicron BA.2 subtype, more testing is needed to determine.

Although infection with the BA.2 subtype can be confirmed positive, more testing is required to determine that the infection is the BA.2 subtype

The Omicron BA.2 subtype appears to be more contagious than the previous mutated virus, although there is no data to suggest that it will be more severe.

What is BA.2?

When a virus mutates to create a new variant, it usually splits into different subtypes. For example, there are as many as 200 different subtypes in the Delta strain.

The Omicron variant is same, which already has subtypes including BA.1, BA.2, BA.3 and B.1.1.529.

BA.1 is the most prevalent subtype, and the World Health Organization says nearly 99 percent of infections in viral DNA received by the Global Initiative for Sharing Influenza Data (GISAID) have been sequenced as BA.1 (as of January 25th, 2022).

Half of the world's new coronavirus cases are Omicron now

The BA.2 subtype was found in sequences uploaded to the database from the Philippines last November, but its original source could not be determined.

Where did BA.2 spread?

The World Health Organization (WHO) said on February 2 that 57 countries had detected the Omicron BA.2 subtype.

The BA.2 subtype already accounts for the majority of confirmed cases in places such as the Philippines, Nepal, Qatar, India and Denmark, and is increasing very rapidly elsewhere, the WHO said.

According to the Statens Serum Institut in Denmark, about half of the new confirmed cases in the country are infected with the BA.2 subtype.

India is also another country where the BA.2 subtype has rapidly replaced the Delta and Omicron BA.1 subtypes, and has become the main infection variant in several states within the country, driving the country's recent third wave of outbreaks.

The Philippine Department of Health said that the BA.2 subtype already dominated the samples received by the end of January.

The UK Health Security Agency says there have been more than 1,000 confirmed cases in England of the BA.2 subtype.

British health authorities have listed BA.2 as a "mutant strain under investigation", meaning authorities will be watching its development closely, but there is currently no undue concern.

BA.2 infections are also increasing rapidly in Germany, overtaking BA.1 and Delta, said Dr Meera Chand from the UK's Health Security Agency.

BA.2 is more contagious?

India is also a country where the BA.2 subtype is rapidly replacing other mutated viruses

A survey of 8,500 households and 18,000 people by the Danish Serum Institute found that BA.2 was significantly more infectious than BA.1.

BA.2 resulted in higher rates of breakthrough infections in people who received the two and three-dose vaccines than other mutant strains, the report said, although those who were vaccinated were less likely to transmit the virus to others.

Another survey conducted in the UK also found that BA.2 was more contagious than BA.1.

But according to a preliminary assessment, there is no evidence that the vaccine is less effective against any one subtype.

Is BA.2 more dangerous?

There is no data to suggest that BA.2 infection is more severe than any previous variant of the Omicron subtype.

"From countries where BA.2 cases surpassed BA.1 cases, we haven't seen any significant increase in severe hospitalizations," said Boris Pavlin of the WHO's COVID-19 response team.

He said that even if BA.2 replaced BA.1, it would not have much impact on how the global outbreak develops and patients are treated.

"It's not expected to have much impact, but we need more data," Dr.Pavlin said.

UK health authorities list BA.2 as “under investigation”

Like other mutated viruses, experts believe the vaccine will remain effective and avoid severe illness, hospitalization and death.

"Vaccines are effective in preventing severe disease, including Omicron," Pafferin said.

"So far, there is not enough evidence to suggest that BA.2 causes more severe illness than BA.1, but the data is limited and the UK Health Safety Agency will be watching closely," Zander said.

"We still need to be more vigilant, get more people vaccinated, continue to have regular rapid screening tests, and do PCR tests if they have symptoms."

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