It’s time to worry about the Delta variant

The Delta variant (also known as B.1.617.2) was first identified in India earlier this spring. It’s now known to spread more easily than any other variant found so far and evade immunity from a prior COVID-19 infection. Scientists are also investigating the variant’s potential to more easily cause severe disease—as well as links to a “black fungus” that has become a secondary epidemic in India.

Harvard epidemiologist William Hanage called the variant “really, really anxiety-inducing,” STAT’s Andrew Joseph reports. (If you’d like to read more on the biology of this variant, Joseph’s article provides a useful overview.)

The Delta variant was first identified in the U.S. in April. It’s making up a small fraction of new cases at the moment, but is spreading rapidly: from an estimated 1.3% of cases on May 8, to 2.5% of cases on May 22, to 6.1% of cases on June 5. The June 5 estimate comes from CDC’s Nowcast predictions, which extrapolate from the most recent available sequencing data (typically reported with a lag of two weeks or more.)

The share of cases caused by this variant appears to be doubling every two weeks, which means that Delta could become the dominant variant here this summer. Some data suggest that domination could happen within a month—a dashboard run by the testing company Helix puts Delta at 10% of new cases as of May 31, suggesting an even faster transmission rate for the variant.

Helix scientist Alexandre Bolze wrote on Twitter that Delta could become dominant “next week or next 2 weeks” based on these trends.

Other variant trends also support Delta’s dominance. This variant, along with Gamma (or P.1, the variant first identified in Brazil), appears to be outcompeting other variants of concern in the U.S. Alpha (or B.1.1.7) has now plateaued at around 70% of U.S. cases, according to CDC data. The variants found in California and New York, both of which made up more than 10% of new cases earlier in the spring, are now declining.

While the CDC is not yet publishing data on Delta’s prevalence in individual states, we can assume that state-by-state variant trends—especially in those states where Delta cases were first identified—are reflecting the variant’s rise on a national level.  

Many experts are now looking at Delta’s spread in the U.K. as a portent for its spread here. The variant has become dominant in the U.K., thoroughly outcompeting Alpha, and is driving a new surge—even though over half of the British population has received at least one vaccine dose. In fact, the U.K. has delayed its full reopening plans by a month due to this case resurgence.

The COVID-19 vaccines currently in use in both the U.K. and the U.S. do work well against Delta, especially the Pfizer and Moderna vaccines—and especially after a full two-dose regimen is complete. But anyone not yet vaccinated is highly vulnerable to this variant. In the U.K., the current case surge is driven by young adults and teenagers who aren’t yet eligible for vaccination.

As physician and public health expert Vin Gupta put it: “Being unvaccinated on June 9, 2021 is much more risky to your own wellbeing than being unvaccinated on June 9, 2020.” And the longer one waits, the riskier this condition becomes.

The Delta variant should serve both as an additional reason for those in wealthy nations who aren’t yet vaccinated to get their shots—and a reason for wealthy nations to share doses with the rest of the world.

More variant data

• National numbers, September 17September 17, 2023
  For the second week in a row, available data suggest that the current COVID-19 surge may be turning around, or at least heading for a plateau. But there’s still a lot of coronavirus going around—and this will likely remain true through the winter respiratory virus season.
• New data on BA.2.86 suggest the fall booster may work wellSeptember 10, 2023
  Since BA.2.86 emerged a couple of weeks ago, scientists around the world have been racing to evaluate this variant. Several teams posted data in the last week, and the news is promising: while BA.2.86 does have an advantage over past variants, the lab findings suggest that vaccines (including the upcoming boosters) and past infections provide protection against it.
• Wastewater surveillance is crucial for tracking new variants, BA.2.86 shows usSeptember 3, 2023
  This week, the health department in New York City, where I live, announced that they’d identified new variant BA.2.86 in the city’s wastewater. I covered the news for local outlet Gothamist/WNYC, and the story got me thinking about how important wastewater surveillance has become for tracking variants.
• Variant Q&A: Why scientists are concerned about BA.2.86, and which questions they’re still investigatingAugust 27, 2023
  Last week, I introduced you to BA.2.86, a new Omicron variant that’s garnered attention among COVID-19 experts due to its significant mutations. We’ve learned a lot about BA.2.86 since last Sunday, though there are many unanswered questions to be answered as more research is conducted.
• BA.2.86 is the latest variant to watch; send me your questionsAugust 20, 2023
  Last week, several variant experts that I follow on Twitter started posting about a new SARS-CoV-2 variant, first detected in Israel. They initially called it Omicron BA.X while waiting for more details to emerge about the sequence; it’s now been named BA.2.86.