Starting in May at the very latest, the Delta variant of COVID began surfacing in the U.S. The CDC states that the Delta variant is more than twice as contagious as other variants of the virus. Additionally, they state that transmission among those who are unvaccinated is most common, as people who are not vaccinated are more likely to become infected and spread the virus. 

“Delta is currently the predominant variant of the virus in the United States,” reads the CDC website. 

Additionally, the Pfizer vaccination was fully approved by the FDA for individuals aged 16 and older on Aug. 23. Following the announcement, President Biden urged Americans to get the vaccination as quickly as they could. 

The Biden administration also recommended a COVID booster shot for all Americans eight months after their second dose of the Pfizer or Moderna vaccine. However, the FDA is still investigating if a booster shot is safe and effective. 

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 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 who will run tests with harmless “pseudoviruses” designed to impersonate the variant’s characteristic mutations.