‘Son’ of COVID-19 Delta Variant on Scientists’ Radar

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The UK Health Security Agency says that as of September 27, about 6% of sequencing tests in the UK tested positive for the Delta descendant—AY.4.2—which some scientists estimate may be 10% more infectious than original Delta.

There’s no cause for alarm just yet, but there is cause for concern. A subtype of the Delta variant of COVID-19—AY.4.2—which might be about 10% more infectious than the original Delta is contained mostly in the UK, for now. It’s uncertain how much more it can spread there, but it is spreading.

A report issued last Friday by the UK Health Security Agency says that the agency is monitoring AY.4.2 more closely. The report states that “this sublineage is currently increasing in frequency. It includes spike mutations A222V and Y145H.” About 6% of the sequencing tests in the UK as of September 27 found AY.4.2. The report states that “this estimate may be imprecise due to known sequencing issues…. Further assessment is underway.”

Francois Balloux, PhD, director at the University College London Genetics Institute, said on Twitter on Saturday that there have been 3 cases in the United States and that in Denmark, which has a vigorous sequencing system, “it reached a 2% frequency but has gone down since.” (Balloux has reportedly said that neither the A222V nor the Y145H mutations have been found in other variants of concern.)

Scott Gottlieb, MD, the former head of the Food and Drug Administration, said on Twitter Sunday that there’s “no immediate cause for alarm” about the AY.4.2. variant, but added that “urgent research” is needed “to figure out if this Delta plus is more transmissible” and can evade immunity.

Gottlieb called for a robust system to identify and characterize new variants. “This needs to be a coordinated, global priority for COVID same as similar international efforts have become standard practice in influenza,” he Tweeted.

Viruses mutate all the time. That’s what viruses do. So far, according to Scipps University's Outbreak.info, the Delta variant has averaged about 2 mutations a month; 56 in total. But at the moment, AY.4.2 is the one that concerns the scientific community the most.

Jeffrey Barrett, DPhil, the medical genomics group leader at the Wellcome Trust Sanger Institute, a not-for-profit genomics and genetics research institute, recently Tweeted that “AY.4.2 hasn’t yet spread much outside the UK, so could be a fluke (no biological advantage), but given that its apparent advantage is modest, it needs to really get established somewhere to overcome stochasticity of small numbers. That is, landing 20 Delta infections in a place with only Alpha almost guarantees that it will go on to complete replacement, whereas 20 AY.4.2 landing in an existing Delta epidemic may well fizzle.”

AY.4.2 certainly concerns Kevin Kavanagh, MD, a member of Infection Control Today®’s Editorial Advisory Board. “There is no doubt that while we celebrate and throw caution to the wind, with Delta infections rapidly decreasing in many areas of the United States, quietly and unseen SARS-CoV-2 is desperately trying to mutate in order to wreak further havoc,” says Kavanagh. “It is like watching a science fiction horror movie. I cannot tell you how it is going to end.”

Barrett seems to agree, Tweeting that the appearance of AY.4.2 “suggests the virus still has evolutionary paths to higher transmissibility open to it, and there are millions of Delta cases around the world without much sequencing coverage.”

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