Delta and Gamma are starting to dominate

This week, the CDC titled its weekly COVID-19 data report, “Keep Variants at Bay. Get Vaccinated Today.” I love a good rhyme, but the report also makes a valuable point: vaccinations not only protect individuals from coronavirus variants, they also reduce community transmission—slowing down future viral mutation.

Delta, or B.1.617.2, is particularly dangerous. As I’ve written before, this variant spreads much more quickly than other strains of the coronavirus and may cause more severe illness, though scientists are still investigating that second point. Thanks to this variant, it’s now much more dangerous to be unvaccinated than it was a year ago.

The Delta variant was first linked to a surge in India, but it’s now become dominant in the U.K., Russia, Indonesia, and other countries. As Eric Topol recently pointed out on Twitter, the variant’s dominance has led to sharp rises in cases—and in deaths—for these nations.

The U.S. is somewhat distinct from the U.K., though, because we had a more diverse group of variants circulating here before Delta hit. In the U.K., Delta arrived in a coronavirus pool that was 90% Alpha (B.1.1.7); here, the Alpha variant peaked at about 70%, with several other variants of concern also circulating.

In other words: we can’t forget about Gamma. Gamma, or P.1, was first identified in Brazil late in 2020. While it’s not quite as fast-spreading as Delta, it’s also highly transmissible and may be able to more easily re-infect those who have already recovered from a past coronavirus infection.

The Gamma variant now causes an estimated 16% of cases in the U.S. while the Delta variant causes 21%, per the CDC’s most recent data (as of June 19). Both are rapidly increasing as the Alpha variant declines, now causing an estimated 53% of cases.

A recent preprint from Helix researchers suggests an even starker change in the U.S.’s variant makeup. Helix’s analysis shows that Alpha dropped from 70% of cases in April 2020 to 42% of cases, within about six weeks.

Delta will certainly dominate the U.S. in a few weeks, but Gamma will likely be a top case-causer as well. Other variants that once worried me—like those that originated in New York and California—are getting solidly outcompeted.  

The TL;DR here is, get vaccinated. Don’t wait. Tell everyone you know.

More variant reporting

  • National numbers, January 29
    At the national level, COVID-19 spread appears to be approaching another plateau. New cases and hospitalizations (as reported by the CDC) are still in decline, but their descent is slowing: reported cases dropped by 11% this week, compared to 24% last week.
  • National numbers, January 22
    National COVID-19 metrics continue to suggest that the U.S. is coming out of its holiday surge, though some parts of the country may face increased transmission as the Omicron variant XBB.1.5 spreads.
  • Looking ahead to the big COVID-19 stories of 2023
    As someone who’s been reporting on COVID-19 since the beginning, a new year is a good opportunity to parse out what feels like an eternity of pandemic reporting. So this week, I reflected on the major trends and topics I hope to cover in 2023—both building on my work from prior years and taking it in new directions.
  • National numbers, January 15
    Last week, I wrote that a combination of holiday travel/gatherings and the latest Omicron subvariant, XBB.1.5, was driving a winter surge. This week, COVID-19 metrics suggest that the surge may have peaked, though we’ll need more data to say for sure—and XBB.1.5 remains a concern.
  • XBB.1.5 FAQ: What you should know about the latest Omicron subvariant
    XBB.1.5 is the latest Omicron subvariant to spread rapidly through the U.S. It is, of course, more transmissible and more capable of evading immunity from past infections than other versions of Omicron that have gone before it, as this lineage continues mutating. Scientists are still learning about XBB.1.5; it emerged from the U.S. during the holiday season, which has posed surveillance challenges. But we know enough to say that this variant is bad news for an already overstretched healthcare system.

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