All you need to know about AY.4.2 variant of Coronavirus

It isn’t yet clear what specific advantage these mutations confer to AY4.2 that aids its spread. However, in terms of its severity, it is still as potent as Delta.

Hyderabad: Since the invasion of Coronavirus last year, the virus has, in a short span of time, evolved into many avatars, including the seemingly infectious delta. Latest one in the long list of Coronaviruses is AY.4.2, which has been termed as a ‘lineage’. The labels were given to variants of the Covid evolutionary tree to illustrate their relatedness. There are now 75 AY lineages identified, each with different additional defining mutations in their genome. One of these – AY.4 – has been steadily growing in proportion in the United Kingdom over the last few months, accounting for 63% of new UK cases in the last 28 days.

To date, 96% of all AY.4.2 cases have been in the UK, but it has been found in 42 other countries. In the US, it accounts for less than 0.5% of all sequences identified so far—but has been spotted in 33 States.

What is it?

AY.4.2 – a sub-lineage of AY.4 – was first noted at the end of September, though it appears it surfaced in the UK around June. It carries two additional mutations, Y145H and A222V that affect the spike protein. The spike protein is a key part of the virus’s outer surface and is the part of its structure that it uses to get inside cells.

This mutation is within an ‘antigenic supersite’ of the spike protein – a part of the protein that antibodies frequently recognise and target. This part of the spike protein has already been modified once before by a mutation in delta’s genetic material, and that this possibly contributes to delta’s greater ability to escape immunity, as antibodies have a harder time targeting it as a result. 

Where did it come from?

The origins of AY.4.2 can be traced back to April 2021. The researchers sequenced two samples connected via travel history to India.

At the time, the lineage circulating in India was B.1.617, but the cases researchers had sampled didn’t match this. It was classified as B.1.617.2, one of three main sub-lineages of B.1.617, and which was later named ‘delta’ by the World Health Organisation.

‘AY’ is a further evolutionary step forward from here. Once a lineage’s labelling gets five levels deep, a new letter combination is started to avoid the name getting too long.

So the ‘AY’ forms of the virus aren’t vastly different from what’s come before, even though their labelling is different. They are all sub-lineages of ‘delta’.

Is AY.4.2 a threat?

Despite introduction into several European countries, AY.4.2 has failed to take hold, dropping off the radar in Germany and Ireland – though it is lingering in Denmark.

This would suggest its ability to get around immunity isn’t any greater than delta’s. Equally, it might just be that there wasn’t enough of AY.4.2 arriving in these places for it to take hold.

It is too early to tell if this is the beginning of the next dominant lineage. Clearly, though, its emergence shows that there’s a continued need for genomic surveillance of the virus.

Is it more transmissible than Delta?

According to experts, it is still unclear whether it is more transmissible or whether it is more capable of evading any immunity that we have through vaccination.

They have warned that the spread of the variant could be the result of a number of factors, including public health measures set out by governments or adherence to those measures.

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