After last week’s backsliding, the prevalence in D.C. has dropped by roughly an equal amount as last week’s increase. The city as a whole, and all Wards except for Ward 5, have dropped below the German rollback threshold of 50 new cases per 100,000 per week (0.05% in the second column below):
|Ward||one week prevalence||one week % pos||two week prevalence||two week % pos|
Wards 2, 3, 4, 6, and 7 all had substantial decreases in the number of cases, and the percent positive rate decreased for those wards, so this doesn’t appear to be an artifact of testing. The not-so-good news is that the prevalence is still too high for things like returning most children to schools (a one-week prevalence of 0.007%, column 2, and a two-week prevalence of 0.014%, column 4, would be equal to a daily new case rate of 1 per 100,000 people). Here’s why:
Low prevalence is not foolproof–it is absolutely not a vaccine, but it does keep infections low enough, such that we can mount an effective test and trace response, as well as survive the occasional bouts of stupid behavior.
To put an infection rate of 1/100,000 in the context of schools, we can look at D.C.’s public schools (DCPS). In its entirely, DCPS staff, students, and teachers number close to 55,000 (note that this doesn’t include the charter school system which is about 90% the size of DCPS). To keep the math simple, we’ll round to 50,000 DCPSers, which is about seven percent of D.C.’s total population. So, if D.C. has 50 cases per week, and seven percent of those cases affect someone in DCPS, we would expect two cases per week, give or take.
Two key points here. First, we will never not have COVID-19 cases in DCPS, even at a really low prevalence; without a vaccine or a very rapid, on-site testing scheme, a COVID-free school system isn’t happening. Second, we can manage a few cases per week in the schools. Most students and schools wouldn’t be have to be sent home or closed. We could ‘flood the zone’ with testing and tracing to find related cases in and out of the school system. But seven to ten times that amount, which is where D.C. is right now in terms of prevalence, and we’re quite strained in our ability to test and trace (remember DCPS is only seven percent of the city; D.C. also needs to deal with 93% of people not in the DCPS system). Likewise, at the current prevalence, it’s possible one or more schools get hit hard, requiring shutting down the entire school. And of course, all of this assumes that there wouldn’t be some spread within schools, so these are probably low-end estimates of the weekly number of cases if schools were open.
(Since D.C.’s charter school system is about the same size as DCPS, we can double this number if/when they return).
Thankfully, we’re not seven to ten times higher now, we’re ‘only’ about six times higher than 1/100,000 daily positives. But cases will happen, and I don’t think, based on the data DC Health is releasing, we have the capacity to run most of these cases down with contact tracing.
So there has been some improvement, but even the ‘best’ wards (in terms of COVID-19 prevalence) aren’t there yet. As I routinely remind readers, we are four to six weeks away from returning to normal-ish, but we intentionally remain four to six weeks away from safely returning to normal-ish because we’re unwilling to do what it takes to make that happen.
Anger is still the appropriate emotion.