Stealth Omicron: What is the fast spreading Omicron BA.2 subvariant? 27th January 2022 – Posted in: Virus – Tags: ,

A new sub-strain of the Omicron variant called “stealth omicron” has been detected in more than 40 countries and can escape even RT-PCR testing, the UK has said. Sub-strain BA.2, commonly called “stealth omicron”, has raised fears of a stronger wave across Europe. So what is this Omicron subvariant and how dangerous is it? Here’s what we know so far. Read also: What is the usual recovery period for Omicron? Here’s what the Centre says

According to the World Health Organisation, the Omicron variant has three subvariants: BA.1, BA.2 and BA.3. While the BA.1 subvariant is dominant among Omicron infections reported worldwide, the BA.2 subvariant is said to spread rapidly. It has been found in a substantial fraction in India, as the peak of Covid-19 is likely to arrive in the next fortnight. Read also – Dakshina Kannada imposes new restrictions, makes 7-day isolation mandatory for students in Kerala | Guidelines here.

“Omicron is now in community transmission in India and has become dominant in multiple metros, where new cases have been increasing exponentially. The BA.2 lineage is in a substantial fraction in India and S-gene based screening is, therefore, likely to give high false negatives,” INSACOG said. Read also: Explanation: New Covid-19 guidelines for RT-PCR testing; watch video

Countries where Stealth Omicron cases have been detected

In addition to the UK and Denmark, cases of sub-strain BA.2 have been detected in Sweden, Norway and India. Scientists in India and France have also warned about the sub-strain, fearing it could overtake sub-strain BA.1. As of 10 January, the UK had identified 53 sequences of sub-strain BA.2, and updated figures will be published on Friday.

Is the Sub-strain BA.2 a cause for concern?

According to researchers, although the BA.2 sub-strain shares 32 strains with BA.1, there may be more than 28 unique mutations in it, according to a Fortune report. The researchers say BA.1 has one mutation – the deletion in the “S” or spike gene – that shows up in PCR tests, making it easier to detect Omicron. BA.2, on the other hand, does not have the same mutation, making it difficult to detect.

“However, the BA.2 sublineage lacks this deletion in the spike, so it can be picked up by using most PCR kits that are used for RT-PCR testing. This new BA.2 sublineage is called “stealth omicron” because it lacks the deletion that allows it to be picked up by PCR testing. BA.2 appears to be the main omicron lineage in parts of India and the Philippines, and there is evidence that it is growing compared to BA.1 in Denmark, the UK and Germany,” Prof Sunit K Singh told India Today.

Does this make PCR tests ineffective against stealth Omicron?

Although the BA.1 subtype can sometimes escape RT-PCR tests, experts say these tests remain the gold standard for detecting the virus. “The laboratory RT-PCR test is the gold standard test and there is no difference in sensitivity or uptake rate between Omicron or the earlier Delta when using this test. The 30-plus mutations in the spike protein in the Omicron variant make no difference in sensitivity using currently available test kits,” Dr Harsh Mahajan, MD and founder, chief radiologist at Mahajan Imaging, told India Today.

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