On 26th November 2021, B.1.1.529 variant or Omicron was labeled as a variant of concern (VOC) by the World Health Organization (WHO) on the endorsement of its Technical Advisory Group on Virus Evaluation. The first reports of omicron were received from Africa (1). The infection caused by omicron has spread rapidly and the infections instigated by this variant have been reported in 85 countries till 15th

December 2021 (2). The fears surrounding the Covid-19 have again fueled the spread of Omicron globally like previous other VOC. Here, we will discuss the nature of the omicron BA.2 sub-variant, its transmissibility, and the protection of vaccines against it.



Studies have reported that 3 lineages of the omicron variant have evolved namely BA.1, BA.2, and BA.3. Although BA.1 is the utmost popular lineage, BA. 2 lineage is being called “Stealth Omicron”. The reason for this name is the missing target gene in BA.1 lineage is not missing from BA.2 lineage. Due to this missing target gene, the identification of omicron is common in the PCR test (3-6). The monitoring of this sub-variant is carried out by scientists in the same way as they have conducted for previous variants by tracking the submitted viral genomes in the public databases including GISAID.

Trevor Bedford who is a computational virologist working at Fred Hutchinson Cancer

Center and pursuing the evolution of the virus behind Covid-19 based on the sequencing data of GISAID posted on his Twitter that the case of BA.2 reported in Denmark

accounts for 82% of total cases. In the UK, it accounts for 9% of the cases and in US, the percentage of BA.2 cases is reported to be 8% (7). The spike mutations at positions 69 to 70 are missing in BA.2 variant because of which S gene failure does not occur which makes BA.2 sub-variant more difficult to be recognized by PCR test.


The Center for Infectious Disease Research and Policy published a study reporting the transmissibility of the BA.2 sub-variant is considerably higher than the initial omicron variant. According to the earlier reports, the infection-causing property of the BA.2 variant is more than the initial spreadable BA.1 variant (8). A study conducted by

  Danish health officials reported that the rate of transmission of the BA.2 variant is 1.5

times more than the initial BA.1 omicron variant (9). According to WHO, the probability of the BA.2 variant to spread within the household is estimated to be 39% than the original BA.1 dominant variant which is estimated to be 29%.

The preliminary analysis conducted by the UK Health Security Agency, England by contact tracing during the duration of 27 December to 11 January suggests that the household transmission of BA.2 infected people is higher (13.4%) in comparison to the

other cases of omicron (10.3%) (10). This raises the question that would people infected with BA.1 variant to remain safe from BA.2 variant. The same has been a source of concern in Denmark and the countries already facing a high count of cases due to the BA.1 variant and reporting an increase in BA.2 cases.



The transmissibility of the omicron variant is more advanced than the prior variants including the delta variant contributing to its widespread globally and the mutation present in the genome of omicron has also given it an edge to elude the protection provided by the earlier coronavirus infection or through the vaccination. Worries have increased with the news of omicron sub-variant that is more contagious than the original variant.

The UK Health Security Agency has conducted a survey using contact tracing and found that the spread of the sub-variant BA.2 has been more in England in comparison to

BA.1. However, the difference in the effectiveness of vaccines could not become evident from the preliminary assessment for BA.1 and BA.2. The effectiveness of the vaccine after 25 plus weeks of 2 doses was found to be g% for BA.1 variant and 13% for BA.2

variant. This effectiveness increased following the third vaccine after two weeks for BA.1 to 63% and for BA.2 to 70% (la

The Danish study also supports the survey of the UK Health Security Agency that

protection is still provided by vaccines against infection and further spread of the virus. Nevertheless, the Danish study also reported that the degree of vaccine protection is less for BA.2 variant in comparison with BA.1 variant. The study reported a reduced

 transmission and susceptibility in booster-vaccinated people for both the sub-variants of omicron in comparison to the people who have had two doses of vaccines. The effective

  transmission of the virus in vaccinated people supports the previous findings that immune evasive properties are present in the omicron variant (12-15).

Still, reduced transmission and susceptibility have been reported for both fully

vaccinated and booster vaccinated people in comparison to unvaccinated indicating that vaccine effectiveness is significantly present. When talking about the comparison between sub-variants of omicron for vaccine effectiveness, the study reported that susceptibility was higher for BA.2 sub-variant in all three unvaccinated, booster-vaccinated, and fully-vaccinated people in comparison to BA.1 indicating that the transmission of BA.2 is inherently greater (9).


The sub-variant BA.2 has still not yet been labeled separately frill omicron as a variant of concern by WHO. Though, WHO officials speculate that with the spread of the omicron variant, there are chances that new variants can emerge globally at an extraordinary rate. The sub-variant BA.2 has become dominant rapidly in Denmark affecting all groups regardless of gender, size of households, age, and status of

vaccination. The sub-variant BA.2 of omicron is more transmissible but it spreads less in vaccinated people. What is more reassuring is the knowledge that the degree of infection is milder with BA.2 variant when compared with the delta variant. This is because of the protection offered by the vaccines against severe infection and hospitalization. It is

hoped by scientists and leaders of public health worldwide that mass omicron exposure and vaccination will help to develop immunity in populations resulting in fewer people falling prey to the virus that will eventually make the coronavirus less troublesome for society.


  1. CDC COVID-19 Response Team. SARS-CoV-2 B.1.1.529 (Omicron) Variant —United States, December 1-8, 2021. Morb Mortal Wkly Rep. 2021 Dec 17;70(50:1731-4.
  2. Weekly operational update on COVID-19 – 21 December 2021 [Internet]. [cited 2022 Feb 8]. Available from:
  3. Sample I, Walker P. Scientists find ‘stealth’ version of Omicron that may be harder to track. The Guardian [Internet]. 2021 Dec 7 [cited 2022 Feb 8]; Available from:


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  2. Latif AA, Mullen JL, Alkuzweny M, Tsueng G, Cano M, Haag E, et al. BA.2 Lineage Report [Internet]. [cited 2022 Feb 8]. Available from: https://outbreak.infoisituation-reports?pango=BA.2
  3. Latif AA, Mullen JL, Alkuzweny M, Tsueng G, Cano M, Haag E, et at BA.3 Lineage Report [Internet]. [cited 2022 Feb 8]. Available from: https://outbreak.infoisituation-reports?pango=BA.3
  4. The Guardian. Omicron: what do we know about ‘stealth’ subvariant BA.2? The Guardian [Internet]. 2022 Jan 31 [cited 2022 Feb 8]; Available from: https://www.theguardian.comiworld/2022/jani3Vomicron-what-do-we-knowabout-stealth-subvariant-ba2
  5. Schnirring L. Study suggests BA.2 COVID-19 subvariant more contagious [Internet]. CIDRAP. 2022 [cited 2022 Feb 8]. Available from: https://www.cidrap.umn.eduinews-perspective/2022/01/study-suggests-ba2- covid-19-subvariant-more-contagious
  6. Lyngse FP, Kirkeby CT, Denwood M, Christiansen LE, Molbak K, Moller CH, et al. Transmission of SARS-CoV-2 Omicron VOC subvariants BA.1 and BA.2: Evidence from Danish Households [Internet]. medRxiv; 2022 [cited 2022 Feb 8]. p. 2022.01.28.22270044. Available from:


  1. Broder T. Omicron subvariant BA.2: what we know so far [Internet]. Guidelines. 2022 [cited 2022 Feb 8]. Available from: anti cle

UK Health Security Agency. COVID-19 variants identified in the UK [Internet]. GOV.UK. [cited 2022 Feb 8]. Available from:

  1. Lyngse FP, Mortensen LH, Denwood MJ, Christiansen LE, Moller CH, Skov RL, et at SARS-CoV-2 Omicron VOC Transmission in Danish Households [Internet]. medRxiv; 2021 [cited 2022 Jan 27]. p. 2021.12.27.21268278. Available from: https://www.medrxiv.orgicontent/10.1101/2021.12.27.21268278vi
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14.  Ferguson N, Ghani A, Cori A, Hogan A, Hinsley W, Volz E. Report 49 – Growth, population distribution and immune escape of Omicron in England [Internet]. Imperial College London; 2021 Dec [cited 2022 Feb 8]. Available from: https://www.imperial.acukimedicineidepartmentsischool-public-healthiinfectious-disease-epidemiology/mrc-global-infectious-disease-analysisicovid-19/report-49-omicroni

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