AY.3 COVID Subtype Explained As Delta Variant Spawns Offshoots

AY.3, a subtype of the COVID Delta variant, has sparked headlines in Israel in recent weeks after a spate of infections.

Google data for September 3 shows that rising numbers of people in the U.S. are now searching for information about AY.3, though details about this version of Delta are limited.

On Monday, The Times of Israel, citing Army Radio, reported that two cases of AY.3 had been detected in returning travelers. About a week earlier, The Jerusalem Post had highlighted concerns that AY.3 could lead Israel into another lockdown after several reports of infections.

Israel is not the first country to report AY.3. Various Delta sublineages have been detected in the U.S., U.K., Portugal and Indonesia, among other nations, according to the Pango Network, which is responsible for naming COVID genetic lineages.

As of Friday there were 25 known Delta sublineages around the world. The Pango Network states that the purpose of designating new sublineages is to help researchers track the virus on a finer scale.

Such sublineages may not be functionally different to Delta at all.

Penny Moore and Cathrine Scheepers are virus experts at the National Institute for Communicable Diseases in Johannesburg, South Africa. They told Newsweek: "AY.3 is an example of one of these mutated Delta viruses. This particular version, however, shares the same spike mutations as the regular Delta version.

"There are many Delta versions that are now emerging, usually assigned to AY.x. Some of these have additional mutations in the spike region that we're also monitoring and testing, but many have mutations outside of the spike in different regions of the virus that we are less concerned with in terms of immune evasion."

Richard Lessells, an infectious diseases specialist at the University of KwaZulu-Natal in Durban, South Africa, echoed the point. He told Newsweek that as far as the Delta sublineages go, "none of the changes have any major functional significance" as far as we know.

This does not mean AY.3 is harmless. The sublineage, along with other subtypes from AY.1 to AY.12 and the "original" version of Delta (B.1.617.2) are listed as a variant of concern by the U.S. Centers for Disease Control and Prevention. Delta is associated with increased transmissibility and potential resistance to vaccination.

The Pango Network states that each Delta sublineage should simply be treated as Delta unless the World Health Organization or another public health body states otherwise.

Some of the Delta subtypes do have noticeable differences, however. The "Delta plus" lineage that made headlines in August was AY.1—and displayed an additional mutation known as K417N that could make it better at avoiding an immune response.

Despite this, AY.1 has not gained much of a foothold in the U.S., according to CDC data.

In the week to August 28, the Delta variant accounted for 99.1 percent of COVID cases reported in the U.S. AY.1 made up about 0.1 percentage points of that. The CDC does not currently specify the proportion of AY.3 infections.

COVID sample
Lab workers bag a biological sample at a COVID testing site in Dubai in April 2020. Many different Delta subtypes have been detected around the world. Karim Sahib/AFP / Getty