The highly infectious Delta variant may already be dominant in the US, says leading coronavirus test lab

US coronavirus test
Coronavirus testing continues at the ProHealth testing centers in Jericho, New York on April 22, 2020. J. Conrad Williams, Jr./Newsday RM via Getty Images
  • The Delta variant appears to be the most common coronavirus strain for new US infections, according to testing data.
  • The data comes from Helix, a private testing firm that is partnered with the CDC.
  • The data suggests the highly infectious Delta variant is more common than Alpha, which was previously dominant.
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The highly infectious Delta coronavirus variant that’s spread to more than 96 countries may now be dominant in the US, according to a private testing firm partnered with the Centers for Disease Control and Prevention (CDC).

Alexandre Bolze, senior scientist at Helix, said on Twitter on Tuesday that the number of Americans newly infected with the Alpha variant, which was previously the dominant strain, was falling, accounting for less than 20% of positive tests sequenced by the company on June 25.

Meanwhile, the number of people infected with Delta was rising – “10 days ago, Delta represented 30% of sequences,” he said.

Helix is CDC-backed to help track the emergence of new coronavirus variants, and has funding from the National Institutes of Health (NIH) to process up to 100,000 daily tests across the majority of American states, according to the company. It’s one of several labs sequencing tests in the US, and Bolze’s figures don’t account for tests sequenced elsewhere.

Bolze said on Twitter on June 21 that both the Delta variant, first identified in India, and the Gamma variant, first identified in Brazil, have become more common in the US than Alpha, according to Helix’s data. But Delta was increasing at a faster rate than Gamma in most states, he said. Both are more infectious than the original coronavirus variant and have mutations that can help them avoid the immune response.

Data from Global Initiative on Sharing Avian Influenza Data (GISAID), the world’s central sequencing database, backs this up, showing that throughout June, the proportion of sequences with the Delta variant increased at a higher rate than Gamma in the US, although both were rising.

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The findings haven’t been officially endorsed by the CDC. Dr. Rochelle Walensky, director of the CDC, predicted on June 19 that the Delta variant would become the primary strain in the US within months.

The data – which may not be exact due to the relatively low number of cases in the US, and therefore low numbers of tests sequenced – are likely to be submitted to GISAID and Genbank by the CDC.

The World Health Organization (WHO) said in a report released on Wednesday that it expected Delta to rapidly outcompete other variants worldwide.