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 in California, Florida, Maryland, Massachusetts, Nevada, North Carolina, Rhode Island and Washington state, plus the District of Columbia, have so far spotted at least one case of 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.
The sub-lineage has remained a small fraction of circulating cases in the U.S. for several weeks, but American health officials say they are already ramping up efforts to study the new Delta variant descendant.
“We have teams that are constantly reviewing the genetic sequence data and looking for blips, an increase in a certain proportion or just something that’s completely new,” says 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 that 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. Nationwide, AY.1 has hovered around 0.1% of cases.
“Right now, I think there’s not a lot that we know. But in terms of the risk that it poses to public health, the prevalence is very low in the U.S. and we don’t really anticipate that the substitutions [of AY.4.2] are going to have a significant impact on either the effectiveness of our vaccines or its susceptibility to monoclonal antibody treatments,” said Galloway.
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.”
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