New Delta subvariant AY.4.2 spreads fast in UK, US, Russia, Israel: Everything you need to know


Experts say that given how the Delta variant has predominated samples of Covid-19 globally for more than six months, it was seen as an indication that the novel coronavirus had reached its “evolutionary limit’.

A new subvariant of Delta, the dominant variant now of the novel coronavirus worldwide, has attracted the attention of health authorities after cases linked to it were reported in several countries, especially the UK. Taking on changes is a common occurrence with the novel coronavirus as it makes copies of itself and, while most mutations are harmless, some come along that enhance the transmissibility or lethality of the virus. Although experts say that with the AY.4.2, as the Delta subvariant is called, there is little data available now to support such concerns. Here’s what you need to know.


The AY.4.2 belongs to the same family of mutations that define the B.1.617.2, or Delta, variant of the novel coronavirus that was first identified in India in October last year and was seen as having fuelled the second wave of cases in the country. It is an offshoot of the Delta variant, being a variation on the AY.4 sublineage. The Delta variant, incidentally, now has 55 sublineages.

Reports say that it was first reported in the UK in July this year, but it is in recent days that cases associated with the subvariant have seen a rise. UK health authorities said in a report on October 15 that “AY.4.2 is noted to be expanding in England” and that “this sublineage accounted for approximately 6 per cent of all sequences generated, on an increasing trajectory” per the data available for the week beginning September 27, 2021.


The subvariant is said to contain two major mutations — A222V and Y145H — in its spike protein.


According to, AY.4.2 is a “predominantly UK lineage” and 96 percent of samples that reported this subvariant were sequenced in the UK. But the subvariant has also been reported in the US, Russia and Israel, among other countries.

Russian scientists said the country has seen “isolated cases” of AY.4.2 while authorities in Israel are said to have detected the subvariant in an 11-year-old boy who had flown into the country.

Francois Balloux, director of the UCL Genetics Institute in London, said in a series of tweets that the spread so far of AY.4.2 appears mostly limited to the UK and “remains exceptionally rare anywhere else”.

Citing data from the Indian SARS-CoV-2 Genomics Consortium, Vinod Scaria, a scientist at the CSIR-Institute of Genomics & Integrative Biology, said in a tweet that “we don’t yet have AY.4.2 in the 68,000+ genomes from India” that have so far been indexed by Indian COVID-19 Genome Surveillance.


It has to be noted that AY.4.2 is yet to be designated by the World Health Organisation (WHO), which has identified four variants — Alpha (B.1.1.7, first reported in UK), Beta (B.1.351, South Africa), Gamma (P.1, Brazil), Delta (B.1.617.2, India) — as Variants of Concern (VoC). A VoC designation means that the variant is associated with increased transmissibility, or is seen to cause more severe disease, or is found to decrease the effectiveness of “available diagnostics, vaccines, therapeutics”, WHO says.

There are also Variants of Interest (VoI), of which there are two listed at present — Lambda (C.37, Peru), Mu (B.1.621, Colombia) — which, WHO says, are those that display “genetic changes that are predicted or known to affect virus characteristics such as transmissibility, disease severity, immune escape, diagnostic or therapeutic escape” and to cause “significant community transmission or multiple COVID-19

clusters, in multiple countries”.

Coming back to AY.4.2, researchers across countries are mostly agreed that although it is more infectious, it does not demonstrate any ingredients that should be a cause for immediate worry.

A Russian researcher told news agency Reuters that AY.4.2 may be approximately 10 per cent more infectious than its “parent” variant, that is the Delta variant, and could ultimately replace it, noting at the same time that the process would likely be slow one even as “vaccines are effective enough against this version of the virus, which is not so different as to dramatically change the ability to bind to antibodies”.


Experts say that given how the Delta variant has predominated samples of COVID-19 globally for more than six months, it was seen as an indication that the novel coronavirus had reached its “evolutionary limit”. But as Danny Altmann, immunology professor at Imperial College London, told CNBC while “the hope has been that delta perhaps represented [the] peak mutation performance achievable by the virus, AY.4 may be starting to raise doubts about this assertion”. He added that the subvariant “needs to be monitored and, so far as possible, carefully controlled”.

But for now, experts are of the view that more data would be needed to arrive at any conclusion regarding the threat AY.4.2 represents. Dr Scott Gottlieb, a former US Food and Drug Administration commissioner, said that “there’s no clear indication that it’s considerably more transmissible”, although he, too, stressed on the need to “more quickly characterise these and other new variants”.

On the other hand, the director of the US Centres for Disease Control and Prevention (CDC), Rochelle Walensky, said that while AY.4.2 “has drawn some attention in recent days”, there is no cause for concern as yet in the US.

“At this time, there is no evidence that the sublineage AY.4.2 impacts the effectiveness of our current vaccines or therapeutics,” she said during a White House COVID-19 briefing. But as experts have pointed out, as long as there are unvaccinated people, the virus will continue to evolve.

But Andrew Pollard, head of the Oxford Vaccine Group, which helped to develop the Oxford-AstraZeneca vaccine, said that it is still too early to flag AY.4.2 as the next big threat.

“Discovery of new variants is of course important to monitor, but it doesn’t indicate that that new variant is going to be the next one to replace Delta,” he is said to have told BBC radio, adding that “even if it does, Delta is incredibly good at transmitting in a vaccinated population and a new one may be a bit better but it’s unlikely to change the picture dramatically from where we are today”.