As Delta Sub-Variant AY.4.2 Spreads, How Worried Should We Be?

Data is slowly but increasingly suggesting that the COVID AY.4.2 variant has a growth advantage over other Delta types, according to a genomics expert.

AY.4.2 is an evolution of the Delta AY.4 variant, the latter of which has been widely detected around the world, particularly in the United Kingdom.

AY.4.2 is characterized by two mutations in particular, in its spike genome: Y145H, and A222V. Scientists are still trying to figure out what these mutations might mean for the variant's success.

The Delta offshoot has come under the spotlight over the past several days after experts noted a sharp rise in its prevalence in the U.K. from July onwards.

According to Outbreak.Info, which collects data on the spread of COVID variants from a virus database called GISAID, AY.4.2 accounts for between 7 and 8 percent of recent sequenced COVID samples in the U.K.

Details are still scarce, but it's thought that, based on current data, AY.4.2 has a growth advantage of around 10 percent over other Delta variants.

It has been suggested that this could be down to luck or some sort of fluke, but this is looking increasingly unlikely, Jeffrey Barrett, director of the COVID-19 Genomics Initiative at the Wellcome Sanger Institute, told Newsweek.

"We are one of the groups that has observed a ~10% growth advantage compared to other Delta," he said. "I'd say we can't say for sure yet that that is a true biological advantage, as opposed to a bit of epidemiological 'luck' for this lineage, but the data are now accumulating week-by-week in favour of a small growth advantage."

Things are still hazy as far as the variant's mutations are concerned, however.

"A222V has been seen in a lineage from summer 2020 which spread around Europe pre-Alpha, but there was never strong experimental evidence of what that mutation might do, nor was there consensus it really gave a growth advantage in the wild," Barrett added.

Things are perhaps even less clear regarding Y145H, which hasn't really been seen before. There's no lab data yet on its possible function.

In any case, AY.4.2 is still very rare in the U.S., though the Centers for Disease Control and Prevention (CDC) this week acknowledged that cases had been identified in the country.

In a White House COVID briefing on Wednesday, CDC director Rochelle Walensky said the Delta subvariant has "on occasion" been seen in the U.S. "but not with recent increased frequency or clustering to date," according to the San Francisco Chronicle.

Walensky added there is no evidence that the variant impacts the effectiveness of current COVID vaccines.

And while AY.4.2 may be on the increase in the U.K., this doesn't mean it's going to take over in the same way the original Delta did, according to Oxford Vaccine Group chief Andrew Pollard.

Pollard told BBC Radio this week, as per the New York Post: "Indeed, 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."

COVID sample
A lab worker handles a sample for COVID testing in west London on January 21, 2021. AY.4.2 is mostly spreading in the U.K., sequencing data shows. Justin Tallis/AFP / Getty