Over the weekend, the UK Health Security Agency (UKHSA) and the World Health Organization said they have designated BA.2, one of the four Omicron variant lineages, as under investigation.
The reason for this designation was early signs that the lineage is outcompeting the other three, which in themselves are among the most transmissible already.
Why is BA.2 different?
The Omicron variant comprises four sister lineages. The earliest, detected in South Africa, was the B.1.1.529. Then came BA.1, which is now globally the predominant one, followed by BA.2 and BA.3. It is not unusual for variants to mutate and branch off into such lineages. It happened with Delta, which grew into AY.4.2, which was found in large samples in the UK.
What makes BA.2 different from BA.1 is 28 unique mutations, including 12 in what is known as the receptor binding domain (RBD) – a portion of the virus that has a key role in infection. BA.2 also has 32 shared mutations with BA.1, but the 28 unique ones are not a small number.
To be sure, the number of mutations does not alone determine if the virus’s function changes. They can depend on individual or a certain set of mutations, or even a new combination that may have arisen.
Is it worrying?
{{/usCountry}}Is it worrying?
{{/usCountry}}At the outset, it does not appear so, and the most crucial sign of this may come from India. In submissions by Indian labs recently, BA.2 accounts for 33% of genomes sequenced from patients in the past month. This means the particular offshoot is already present in large numbers in India, at least in some parts of the country.
According to outbreak.info, the Indian regions where most of these samples came from are Assam, Uttar Pradesh and Haryana. At present, none of the Indian regions are reporting a significantly different hospitalisation or death trajectory from others, which means almost all Omicron lineages in India are behaving in a similar manner.
This has also been borne out by Denmark’s experience, where severity estimates have not changed even as BA.2 is estimated to now account for 81% of cases.
Why it must be monitored
That it is outcompeting the other Omicron lineages still makes it worth investigating because scientists need to understand what traits exactly are giving it that advantage. Remember, even Omicron’s transmissibility advantage as a whole has not been well understood. In this light, a change in the variant that makes it even fitter is important to decode.
The other parameters that will be monitored are if it is more resistant, which too can give it a transmission advantage. Imperial College London virologist Tom Peacock, who was among the first to spot Omicron’s vastly mutated nature, said last week that he believes there would be a “minimal difference in vaccine effectiveness against BA.1 and BA.2” and that it is “highly likely” that an infection with BA.1 will protect against a BA.2 infection. More studies are awaited.