In the last couple of weeks, there has been a noticeable increase in the discovery of BA.2 sub-variant of Omicron from several countries, leading to fresh worries about the possibility of another surge in cases. Last week, the UK Health Security Agency flagged this sub-variant and designated it as a ‘variant under investigation’. And, in its latest weekly bulletin, the World Health Organisation noted that a number of countries had reported an increase in the BA.2 sub-variant in the last seven days.
This sub-variant has been present in substantial numbers in India as well, but India is not amongst the countries where the recent increase has been noticed. The BA.2 could possibly be more infectious than the more commonly found BA.1 variety but there is no evidence to suggest that it is more harmful.
BA.2 is one of the several sub-variants of the Omicron which has spread rapidly across the world since November. The Omicron name was given to the B.1.1.529 lineage after it was designated as a variant of concern. Later, it was found that this lineage had small variations of its own, and the three most common were named B.1.1.529.1, B.1.1.529.2, and B.1.1.529.3. For ease of reference, however, these sub-lineages were later re-classified as BA.1, BA.2 and BA.3.
The Omicron sub-variant that has been most common in circulation till now is BA.1. This continues to be the case even now, though the proportion of BA.2 is on the rise. According to the WHO, 98.8 per cent of all Omicron genetic sequences submitted in global databases till January 25 were that of BA.1 variety. BA.2 retains most of the characteristics of BA.1 but has some more mutations that can give it a distinctive characteristic.
“…the BA.2 descendent lineage, which differs from BA.1 in some of the mutations, including in the spike protein, is increasing in many countries. Investigations into the characteristics of BA.2, including immune escape properties and virulence, should be prioritised independently (and comparatively) to BA.1,” the WHO has said.
So far, studies have not showed any distinct advantage of BA.2 over BA.1, particularly in the nature of disease that they cause, but the recent rise in BA.2 cases is likely to put a more intense spotlight on this sub-variant.
The increase in proportion of the BA.2 has been noticed mainly in Europe, most prominently in Denmark, where over 8,300 genetic sequences of this Omicron sub-variant have been identified so far. In fact, in Denmark, BA.2 now comprises almost half of all Omicron cases. The United Kingdom has found 607 samples with this sub-variant, while India has discovered 711 till now. The other countries where BA.2 has been found in abundance are the United States, Norway, Sweden and Singapore.
According to the outbreak.info website, that tracks the prevalence of the different lineages of this virus across the world, BA.2 has so far been discovered in 49 countries.
The BA.2 sub-variant is known to be more transmissible than the BA.1 variety, which could possibly explain its surge in recent days. But as of now, researchers have not noticed any difference in the nature of disease that it causes.
Though these are sister lineages, there are important genetic differences between BA.1 and BA.2. In fact, Statens Serum Institut, Denmark’s main institution on infection diseases, said the difference between BA.1 and BA.2 was greater than the difference between the original Wuhan variant which started the epidemic and the Alpha variant, the first major variant that had become dominant in 2020.
“Such differences can lead to different properties, for instance concerning infectiousness, vaccine efficiency or severity. So far, there is no information as to whether BA.1 and BA.2 have different properties…,” the institute said in a note last week.
“Initial analysis shows no differences in hospitalisations for BA.2 compared to BA.1. Analyses regarding infectiousness and vaccine efficiency etc. are ongoing, including attempts to cultivate BA.2 in order to perform antibody neutralization studies. It is expected that vaccines also have an effect against severe illness upon BA.2 infection,” the note said.
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