I shouldn’t have to say it. But I do.
Nuclear reactors can use “control rods” to control the reaction. Push them in all the way, they’ll slow the reaction so much it will quickly die out. Pull them all the way out, the reaction grows so fast it goes critical — but before it can “go nuke” it melts. Still a disaster.
The “basic” epidemiological model (the SIR model) makes some very basic assumptions, and treats the spread of a disease like COVID-19 in a straightforward manner. It gives rise to the “bell-shaped” curve (the one everyone wants to flatten) we’ve seen in so many news stories.
Of course it’s not “right” — there are too many unaccounted-for factors to believe that. But they also encompass certain purely logical ideas which are known to be correct. Added bonus: the equations are not unlike what you see when you study how neutrons keep the reaction going in a nuclear reactor. The reactor equations are likewise imperfect, but they too encompass some undeniable logical ideas. The most impressive thing they have in common: experience has shown that they both work.
And now to the real point of this post. Pay attention, because this is the real message and it’s worth it. Here it is:
Part 1: How fast a nuclear reaction grows or shrinks depends on where you set the controls.
Part 2: How fast an epidemic grows or shrinks depends on where you set the controls.
Do you think you can remove the control rods from a nuclear reactor and NOT see the reaction grow?
There’s one way you can. Let the reaction run wild. Pull out the control rods enough that it runs hot, but not hot enough to melt, and let it run until it exhausts its fuel. Then you can remove the control rods because there’s not enough fissile material left to sustain a reaction.
You can do the same with an epidemic. Pull out the controls, let it run its course, and eventually there aren’t enough people left to get sick and sustain the epidemic. You may have heard of it: it’s called “herd immunity.” The catch is: nearly everybody gets it, nearly everybody who can die from it does. In the USA, that means maybe about three million people. I don’t like that solution.
Governors Ron Desantis of Florida and Greg Abbott of Texas act like they can re-open their states’ economies, removing restrictions but not suffer an immediate reaction. When the immediate reaction follows, they blame it on anything but removing the control rods from the nuclear reactor. It’s the fault of “young people” in Texas — it’s the fault of migrant workers in Florida — and it’s the “fault” of more testing. They act like there aren’t really more cases — we just found more because we tested more. I’ve already shown how stupid that is.
And these two republican governers have failed to pay attention to what their own data say — because the data for an epidemic (or a nuclear reactor) tells you when it’s safe to remove some of the controls. The Florida data and the Texas data gave a clear answer: NO. But they opened anyway. Florida even pressured one of their own data scientists to change the data and make it look like they were ready when they weren’t — then fired her when she refused.
State governors should look at the data for their own states. They should know it like the back of their own hand. If the reaction is growing (the case load is rising) it will keep rising unless you push in some control rods. If it’s slowing it will keep slowing unless you pull out some control rods. Every time you change the controls, it will change how fast the reaction grows or dies.
The only way to re-open safely is to wait until the rate is low enough AND it’s not growing hotter, then remove controls slowly while remaining constantly vigilant. If the reaction grows fast enough or far enough, restore controls. If not, then it might be safe to try the next small step.
My advice to governors in all states:
— Don’t remove controls until the rate is very low (well below 50 cases per day per million population) and either steady or going down. When you remove controls, the rate will go up — if we’re lucky, not too fast or too far.
— Don’t loosen too many things at once, or you won’t know which controls are working and which aren’t.
— When the reaction heats up, don’t blame hipsters or gen-X or millenials or migrant workers or testing. It sounds like the dog ate your homework.
In the next post (or at least, soon) I’ll explain and run the SIR model, and show you the control rods in action. There will be math. But not too much.
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