What We Know About Delta AY.4.2 COVID Variant as Study Suggests It Causes Fewer Symptoms

The AY.4.2 variant of COVID may be less likely to cause symptomatic infection than other Delta offshoots, according to new data from the U.K.

The finding was presented in the latest report from the U.K.'s REACT study, which has gathered data from community surveys and swab tests since April 2020 to see how the virus is spreading.

The latest study round, conducted between October 19 and November 5, has provided some insights into the spread of AY.4.2, a version of the Delta variant that has been increasingly spreading through the U.K. in recent months.

As part of the latest round, swab tests from 100,112 people were studied. Of those, 1,399 tested positive for COVID.

Experts went on to sequence the positive samples, which yielded 841 lineages. Of those, all of them were the Delta variant or sub-lineages of the Delta variant—the most dominant coronavirus strain in the world, the World Health Organization has said.

Delta AY.4, the U.K.'s most common Delta sub-variant, accounted for 57.6 percent of these sequences, while AY.4.2 made up 11.8 percent.

The study also looked at reported symptoms based on which sub-lineage the person had. According to a data table in the study, people infected with AY.4.2 were less likely to report "classic" COVID symptoms—loss of change of smell or taste, fever, new persistent cough.

"Compared to AY.4, sub-lineage AY.4.2 was less likely to be associated with symptoms," the study states.

According to Professor Francis Balloux, director of the Genetics Institute at University College London, this result could explain why AY.4.2 has spread so much in the U.K.

He tweeted earlier on Thursday: "AY.4.2 causing a lower proportion of symptomatic infections might explain its increase in frequency, with asymptomatic carriers unwittingly transmitting it more often."

However, he added the finding would need to be confirmed and that its statistical significance is "very marginal."

"I think it is too early to say for certain on this data whether AY4.2 is really less likely to cause illness than other variants," Paul Hunter, a professor in medicine at the University of East Anglia, said in a statement to the Science Media Center. "More work is needed. It would be good, however, if this variant was indeed less virulent but it would be wrong to give too much credibility to this observation just yet."

AY.4.2 is identified by two mutations to its spike protein called Y145H and A222V. The spike protein helps the virus to enter human cells.

Data so far has shown that AY4.2. may have a slight growth advantage over other Delta types.

No More Resistant to Vaccines

At the same time, recent U.K. analysis has indicated that AY.4.2 is no more resistant to vaccines than other Delta types.

According to the variant tracking tool Outbreak.info, AY.4.2 has accounted for at least 40,233 COVID cases worldwide as of November 16 since it was first identified in May.

Of these, 37,883 had been reported in the U.K., where the variant has accounted for more than 15 percent of new sequenced samples.

The variant doesn't appear to have gotten much of a foothold in the U.S., where 25 samples had been sequenced from a total of 13 states, Outbreak.info showed on Thursday.

COVID medical worker
A medical worker holds a COVID swab test kit at a testing center at Dublin Airport, Ireland, on January 29, 2021. Cases of the AY.4.2 variant have been rising in the U.K. in recent months. Paul Faith/AFP / Getty