The CDC says it's identified a new Delta-related coronavirus variant in the US, and officials are monitoring it closely

  • A new coronavirus variant, called AY.4.2, is being closely monitored by scientists around the world.

  • AY.4.2 is a descendant of the Delta variant. It has been found "on occasion" in the US, the CDC said.

  • It's not clear yet whether AY.4.2 is actually more transmissible than Delta, or if it has just had some good luck in the UK.

A new coronavirus descendant related to Delta, called AY.4.2, is being closely monitored by scientists in the US, UK, and Israel.

AY.4.2 is still "very rare" in the US, according to the Centers for Disease Control and Prevention.

"It is well below 0.05% of all our sequenced viruses, with less than 10 reported in our database so far," the CDC said in a statement sent to Insider on Wednesday.

Meanwhile, AY.4, the parent lineage of the new variant, "represents around 11% of the Delta viruses in the United States," the CDC said.

While many different AY lineages of the Delta variant have been documented to date, AY.4.2 has caught the attention of virus-watchers around the world recently because it has two changes located on the viral spike protein, which could perhaps give it some advantages. But it's unclear if that's the case yet.

"At this time ... there is no evidence that the sub lineage A.Y.4.2 impacts the effectiveness of our current vaccines or therapeutics," the CDC said.

The UK Health Security Agency said on Friday that AY.4.2 is currently "expanding" in England and is "increasing in frequency" there, representing an estimated 6% of sequenced strains in the country. Israeli health officials reported their first documented case of AY.4.2 on Tuesday.

Former Food and Drug Administration Commissioner Scott Gottlieb said on Twitter over the weekend that "we need urgent research" to figure out how much of a threat the new Delta descendant really poses.

It's possible that AY.4.2 could turn out to be slightly more transmissible than other versions of the virus we've seen so far. But that's no reason to panic.

"This is not a situation comparable to the emergence of Alpha and Delta that were far more transmissible (50% or more) than any strain in circulation at the time," Professor Francois Balloux, Director of the University College London Genetics Institute, said on Tuesday. "Here we are dealing with a potential small increase in transmissibility that would not have a comparable impact on the pandemic."

AY.4.2 has been identified 'on occasion' in the US

Getting a COVID-19 test to travel to the UK - Testing Facility at JFK Airport
Most COVID-19 tests are never sequenced. Thomas Pallini/Insider

"We have, on occasion, identified the sublineage here in the United States, but not with recent increased frequency or clustering to date," CDC director Rochelle Walensky said during a White House coronavirus briefing Wednesday morning, referencing AY.4.2.

(The UK, which has noticed a larger uptick in AY.4.2 cases recently, has been far better than the US at tracking and sequencing coronavirus variants in real time during the pandemic.)

Jeffrey Barrett, a genomics expert leading the COVID-19 initiative at the Wellcome Sanger Institute, said it's still possible that AY.4.2 has just had a bit of "epidemiological luck" in the UK recently.

Professor Balloux agreed.

"In Denmark, the other country that besides the UK has excellent genomic surveillance in place, it reached a 2% frequency but has gone down since," he said of the subvariant.

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