Delta Sub-Variant AY.4.2, Possibly More Contagious Than Delta, Spreads to More States

A sub-lineage of the Delta COVID-19 variant known as AY.4.2 has now spread to more areas of the U.S., monitoring data shows.

According to Outbreak.Info, which uses virus sequencing data from the GISAID database, AY.4.2 has now been identified in four states—North Carolina, Massachusetts, Washington and California—in addition to the District of Columbia, as of October 21.

At present, the sub-lineage is very rare in the U.S. States. In total, five cases of AY.4.2 have been reported so far in the country—one in each of the states mentioned above and the federal district.

Just two days ago, AY.4.2 had only been detected in California, North Carolina and DC.

AY.4.2 is an evolution of the original Delta variant that was first identified in the U.K. and has since become the dominant form of the SARS-CoV-2 virus, which causes COVID-19, around the world.

The new AY.4.2 sub-lineage is one of more than three dozen evolutions of the original Delta variant that have been identified globally.

According to the Centers for Disease Control and Prevention, the Delta variant is highly contagious—scientists think it is more than twice as infectious as previous variants.

The AY.4.2 sub-lineage of Delta contains two characteristic mutations—called Y145H and A222V—on the spike protein of the SARS-CoV-2 virus, which it uses to bind and enter human cells.

It is not currently clear what these mutations might mean for how this particular sub-lineage will behave.

But some researchers have said that AY.4.2 could be slightly more transmissible than the original Delta variant.

Around 16,830 AY.4.2 cases have been detected around the world across at least 28 countries, figures from Outbreak.Info show.

The vast majority of these cases—16,022—have been identified in the U.K., where AY.4.2 was first spotted in April this year.

Experts in the U.K. have noticed a rise in its prevalence there since July, with AY.4.2 now accounting for around seven percent of recent sequenced samples in the past few days.

While there is still a lack of data on AY.4.2, some groups of researchers have said that the sub-lineage may be around 10 percent more transmissible than the original Delta variant based on its recent spread in the U.K.

Jeffrey Barrett, director of the COVID-19 Genomics Initiative at the Wellcome Sanger Institute in the U.K., told Newsweek in an article published Thursday: "We are one of the groups that has observed a [roughy] 10 percent growth advantage compared to other Delta."

"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 favor of a small growth advantage."

While the sub-lineage is spreading in the U.K., experts have said AY.4.2 is not necessarily going to outcompete the original Delta variant.

Christina Pagel, a mathematician at University College London, who specializes in mathematical modeling for health purposes told previously told Newsweek that the potential 10 percent transmissibility advantage of AY.4.2 "isn't great."

"I don't think there's a reason to think AY.4.2 is disastrous," she said, noting that any advantage it has is "not nearly" as bad as the one that Delta had over the Alpha variant, enabling it to become the dominant form of coronavirus.

Illustration of the coronavirus
Stock image showing an illustration of the SARS-CoV-2 virus. iStock