D.C. Is Entering Phase 2 Today, and D.C. Should Wait

Today, D.C. is entering phase 2 of its reopening. The big changes are restaurants can have indoor seating, gyms can reopen with limited attendance, and houses of worship can allow up to 100 people or 50 percent occupancy (whichever is lower). I have a bad feeling about this. While most of the numbers for D.C. are trending in the right direction, with the exception of daily deaths which is holding constant and seems kind of important (though it’s a lagging indicator), they simply aren’t low enough in absolute terms. That is, there are still too many infected people.

To put this in context, D.C. has roughly the same number of new cases per day as does South Korea, which has 71 times the population. D.C. needs to get down to single digits in terms of new cases per day. If we use the number of people who have tested positive over the last two weeks as an approximate count of the number of people who potentially could transmit an infection to the general population*, we realize that the church gathering of 100 people or the restaurant with fifty is not risk-free at all. If we look at the period between June 4 and June 17, here’s the frequency of infected people for D.C. as a whole and by ward:

Ward 1: 0.12%
Ward 2: 0.03%
Ward 3: 0.04%
Ward 4: 0.18%
Ward 5: 0.09%
Ward 6: 0.07%
Ward 7: 0.12%
Ward 8: 0.16%
D.C. total: 0.10%

But these seem low? Well, in Ward 4, there’s a fourteen percent chance that a church gathering of 100 people has one or more infected people; even in Ward 2, that gathering has a three percent chance of having one or more infected people. Using the D.C. average, that 100 person gathering will have one or more infected people five percent of the time.

Now, that is not a transmission rate, just the probability of one or more infected people. Hopefully, people are wearing masks and spacing, though wearing masks in a restaurant seems unlikely, at least while eating. If we could knock down the number of infected people ten-fold, then even in the most affected ward, that 100 person gathering will have one or more infected people less than two percent of the time, down from fourteen percent; in Ward 2, the probability drops to 0.3%.

That’s what we need for safety–less than ten new cases per day. That also means, if there is a rebound, it will be easier to tamp it down again; we also get more time to do so. Critically, that’s how we allow people to return to some sense of normalcy their lives. When group activities are safe enough that we can reliably survive our own stupidity (and no one, not even professionals, is perfect about adherence), that’s when it’s time to relax. Right now, D.C. is close, but not close enough.

Because, as obvious as it sounds, the best way to not get infected is to not be in contact with anyone who is infected.

*Note the phrase “people who potentially could transmit an infection to the general population.” While there still is undercounting (though not like March or April, where obviously cases weren’t being confirmed), as well as asymptomatic and presymptomatic people, many people who are positive are isolating (either by choice or because they’re too sick to be out). Leaving aside household transmission, you have to be out and about to transmit. And if you think I’m being to optimistic about the number of infected people, that only makes my argument stronger.

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5 Responses to D.C. Is Entering Phase 2 Today, and D.C. Should Wait

  1. Pingback: Links 6/23/2020 | naked capitalism

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  4. ProNewerDeal says:

    Mike, I found your blog link on nakedcapitalism iirc. Thanks for writing this interesting blogsite. IMHO during this COVID era there is a shortage of “public intellectuals” with relevant knowledge such as your biologist self writing earnestly & in a manner non-biomedical laypersons understand, & I appreciate it.

    I am trying to guesstimate/reverse engineer your calculation. For i infection rate, n number of people in the gathering, is the P(1 or more infected person in gathering) = 1 – ( (1 – i)^n ) ?

    Eg for Ward 2, i=.03%, n=100,
    P(1 or more infected) = 1 – ( (1 – .0003)^100 ) = 1 – .9997^100 ~2.96% ?

    I would highly appreciate your response. I am a college graduate in a STEM field & took probability & statistics. If I am using the incorrect formula, a mere pointing to the Wiki page would suffice.

    For me this is not theoretical, as a PT job that is on hiatus maybe coming back, & I would like to plug the “Currently Infected” estimate for my County from https://covid19-projections.com/ into the correct formula to estimate an upper limit on my COVID risk in a shift. With an estimate of risk, I can decide what level of risk is worth taking. I suppose I am fortunate that unlike many of our compatriots working Essential Worker roles, if I feel the risk level is excessive I can resign from that PT job – for me the answer isn’t risk COVID vs starvation.

    Thanks & good luck with your blogsite

    • Yes, that’s how I’m calculating the probability. Obviously, it’s an oversimplification (different people have different rates of infection, any one person isn’t randomly sampling the population etc.), but the toy model makes the point that even when seemingly rare, it’s likely you’ll eventually encounter someone with COVID. Stay safe.

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