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

  • More Omicron mutation in South Africa and the U.S.
    As cases rise in the U.S. and other parts of the world, Omicron subvariants are a continued culprit. Experts are watching closely to see if further mutations of the virus may become even more contagious, or may gain the ability to evade immunity from prior infections and vaccinations.
  • How one wastewater plant became a leading COVID-19 forecasting source
    This week, I had a new story published with FiveThirtyEight and the Documenting COVID-19 project about the data and implementation challenges of wastewater surveillance. As bonus material in today’s COVID-19 Data Dispatch, I wanted to share one of the interviews I did for the story, which provides a good case study of the benefits and challenges of COVID-19 surveillance in wastewater.
  • National numbers, April 24
    After weeks of me warning about it, a BA.2 surge is upon us. Nationwide, new COVID-19 cases have gone up for the third week in a row; we’ve seen a 68% increase since the last week of March.
  • Omicron keeps mutating as U.S. cases rise
    As though it’s not already confusing enough to distinguish between Omicron BA.1 and BA.2, more sublineages have popped up in recent weeks as Omicron continues to spread and mutate. Here are two that I’m watching, though they don’t seem to be major causes for concern at this time.
  • The US still doesn’t have the data we need to make informed decisions on booster shots
    Last fall, I wrote that the U.S. did not have the data we needed to make informed decisions about booster shots. Several months later, we still don’t have the data we need, as questions about a potential BA.2 wave and other future variants abound. Discussions at a recent FDA advisory committee meeting made these data gaps clear.

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