What is 'stealth Omicron' detected in over 40 countries?

United Kingdom has stated that a sub-strain of the Omicron COVID-19 variant has been detected in around 40 countries. The BA.2 sub-strain, also known as the “stealth Omicron”, can escape even the RT-PCR test, meant to detect the coronavirus. Omicron has three sub-strains --- BA.1, BA.2 and BA.3. Incident director at the UKHSA Dr Meera Chand 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.” She added, “Our continued genomic surveillance allows us to detect them and assess whether they are significant.”
 
Here’s what you need to know about the stealth Omicron sub-variant:

1. Britain identified 53 sequences of the BA.2 sub-lineage as of January 10 whereas this particular variant has grown rapidly in Denmark. The BA.2 sub-strain accounted for 45 per cent of all COVID-19 cases in Denmark in the second week of 2022.
2. According to initial analysis by Denmark’s Statens Serum Institut (SSI), there is no difference in hospitalisations for BA.2 compared to BA.1.
3. Besides the UK and Denmark, cases of this variant have been reported from Germany, Sweden, Norway and India.
4. According to the UK-based virologist Tom Peacock, “BA.2 appears to be the major Omicron lineage in part of India and the Philippines and there is evidence it is growing compared to BA.1 in Denmark, the UK and Germany”. Peacock shared a Twitter thread by the Cambridge University physicist Cornelius Roemer.
5. Peacock added that there are minimal differences in vaccine effectiveness against the BA.1 and BA.2 variants and it is also highly possible that BA.1 infection will give decent cross-reactivity against the BA.2 infection. He also advised labs working on surveillance or sequencing should keep a close eye on BA.2.
6. Besides the UK and Denmark, cases of BA.2 sub-strain have been detected in Sweden, Norway and India.
7. According to Roemer, BA.2 has become the dominant Omicron variant in India towards the end of December. BA.2 grew from ~5 per cent in mid-December to approximately 50 per cent by beginning of January.
8. “This new sublineage BA.2 is called ‘stealth Omicron’ because it lacks the deletion that allows it to be picked up by PCR tests. BA.2 appears to be the major Omicron lineage in parts of India and the Philippines and there is evidence it is growing compared to BA.1 in Denmark, the UK and Germany,” according to Professor Sunit K Singh.
9. While these strains might escape RT-PCR at times, experts consider that to be the gold standard in detecting the virus.
10. “Lab RT-PCR test is the gold standard test and there is no difference in the sensitivity or pick-up rate between Omicron or the previous Delta while using this test. The over 30 mutations in the spike protein in the Omicron variant do not make any difference in sensitivity using the presently,” MD, Founder and Chief Radiologist of Mahajan Imaging Dr Harsh Mahajan told India Today.

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