Potentially faster-spreading Delta variant, AY.4.2, spotted in 8 states


A potentially faster-spreading “sub-lineage” of the coronavirus Delta variant named AY.4.2 has been spotted by labs in at least 8 states, and health authorities in the United Kingdom say they are investigating a growing share of cases from this strain of the virus.

Labs located in California, Florida and Massachusetts have assisted at least one case of the AY.4.2.

While it may spread somewhat faster, health authorities have not found evidence of more severe illness caused by the variant, and they say current vaccines remain effective against it.

Although the sub-lineage was not present in the U.S., it has been a significant part of the circulating cases for several weeks. However, American officials claim that they have already increased their efforts to investigate the Delta variant descendant.

” We have teams that constantly review the genetic sequence data, looking for blips or an increase in certain proportions or something completely new,” Dr. Summer Galloway (executive secretary) of the U.S. government’s SARS–CoV-2 Interagency Group.

Galloway, who also serves as policy lead on the CDC’s laboratory and testing task force, said U.S. labs began preparing last month to prioritize tests to assess whether AY.4.2 can evade antibodies from vaccinated Americans, or from currently authorized monoclonal antibody treatments for the virus.

That process can take up to four weeks, Galloway said, across several laboratories who will run tests with harmless “pseudoviruses” designed to impersonate the variant’s characteristic mutations.

Scientists have already turned up worrying combinations of mutations in other sub-lineages of Delta called AY.1 and AY.2, which like AY.4.2 have also sometimes been interchangeably called “Delta plus” variants.

Last month, the Biden administration temporarily halted distribution of a monoclonal antibody treatment in Hawaii after estimated cases of AY.1 climbed up to 7.7% in the state. The Food and Drug Administration said lab experiments with AY.1 suggested it was “unlikely” the drug would be effective against the variant.

The state has since resumed use of the antibody treatment, after AY.1 dropped below 5% in Hawaii. AY.1 hovered at 0.1% in the nation.

“Right now, I think there’s not a lot that we know. Galloway said that although it is a risk to public health in the U.S., its prevalence is low and that we do not expect that substitutions [of AY.4.2], will have an impact on the efficacy of vaccines or the susceptibility of monoclonal antibodies treatments.

In the U.K., AY.4.2 has climbed to more than 11% of cases of the Delta variant. Health officials there say the variant does not appear to have led to a “significant reduction” in vaccine effectiveness or an uptick in hospitalizations, but it could be spreading faster because of “slightly increased biological transmissibility.”

“Estimated growth rates remain slightly higher for AY.4.2 than for Delta, and the household secondary attack rate is higher for AY.4.2 cases than for other Delta cases,” said a report published Friday by the U.K. Health Security Agency.

According to the Centers for Disease Control and Prevention, AY.4.2 is less than 0. 05% of circulating cases in the U.S. for several weeks, according to an agency spokesperson. Grouped together, CDC estimates that the Delta variant and its sub-lineages has been virtually 100% of cases in the U.S. for months.

” Even based on data from the U.K. you can see that the transmission advantage is smaller. It’s not like Delta, which as soon as they came in, it was almost a 50[%] to 60% advantage over all previous lineages,” says Dr. Karthik Gangavarapu, a postdoctoral researcher at UCLA’s Suchard group.

Gangavarapu was part of the team to lead Scripps Research’s variant tracking effort at Outbreak.info, which has tracked variants like AY.4.2 as they have emerged in an international database of “sequenced” viruses maintained by a group called the GISAID Initiative. It could be able to transmit a little more, but there could also be other important factors. How high is the immunity of the people in particular locations? How high is the rate of vaccination? Gangavarapu stated that these may have an impact on the spread of the variant.

The largest share of circulating virus in the U.S. remains closely related to the original Delta variant, among samples reported to GISAID. Although scientists have suggested that the next big variant could be a mutation of the Delta variant, Gangavarapu warned that these highly contagious strains are often independent.

Delta variant sub-lineages like AY. 25, AY.3, and AY. 44 also currently make up large U.S. proportions of cases, though not necessarily because they have an advantage over their siblings.

Outbreak.info had previously counted AY.4.2 sightings in at least 35 states. However, Gangavarapu said a bug in the “Pangolin” system used to generate reports of variants had resulted in some false positives for the sub-lineage showing up in some tallies.

New sub-lineages are frequently re-categorized by scientists to “help researchers track the virus” clustered in certain regions, even when they sport mutations that end up having no meaningful impact on the public health risk of the variant.

” We will probably get more data over the next month to see if the U.K. has the same kind of rise in prevalence as we have seen in the U.S.A,” Gangavarapu says.

Alexander Tin

CBS News journalist covering pandemics and public health.

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