New Biobot COVID wastewater concentration data are out, and D.C., along with neighboring Alexandria, VA, have seen a marked improvement. Here’s D.C.:

Here’s Alexandria, VA:

For context, the maximal values for Alexandria and D.C. during the January 2023 peak were 1,306 and 1,222 respectively, while the current values are 536 and 361 respectively. If you’ve read some of my other posts on D.C.’s wastewater, you’ll see that the weekly numbers change, and don’t really settle down for several weeks–as data come in and are processed (which takes time), the data are updated. What this means is the Alexandria surge wasn’t quite as high as previously estimated (65% of peak versus 76% of peak), but the D.C. surge was actually faster, then plateaued for a week, and then declined. Which is good! Declines are good! Though we would like to see the concentration drop to much lower levels (< 100, which would likely be ~ 0.1% of the population is infected).

What’s puzzling is why there was a drop. Unless something really bizarre is going on with the immunology*, there simply haven’t been enough people infected over the last several months, even with the semi-surge, to result in some kind of short to mid-term herd immunity. Instead, I think it’s behavioral changes. In early to mid-August, we had a lot of rainy and cool weather: when people weren’t staying home to stay dry (summer rain in D.C. often is not gentle and pleasant, it’s more like a brief monsoon–including fun things like the occasional tornado watch/warning), they were gathering outside (85F and dry is dining outside weather, 95F and humid–the August usual–is dining inside weather).

While the weather will remain nice for the next month or two, schools are back in session (both K-12 and colleges), so I think we’ll see increases over the next few weeks (though I hope I’m wrong). Anyway, at least we had a decline, which beats the alternatives.

*I could make up some sort of story about the immunology regarding variants etc., but it would be completely unfounded, so there’s no point.