Diseasonality - by Scott Alexander - Astral Codex Ten
I think maybe they’re saying something like that getting a virus like this usually gives you about a year’s worth of immunity before your immune system “forgets” it. I guess this makes sense in the context of eg needing COVID “booster shots” after a few months.
So one possible model is something like: once you get a disease, you’re protected for a while. There’s no particular length of time, it’s a spectrum, absent any external rhythm-setter you would end up like the tropics, where people have epidemics at random times, once a year, twice a year, whatever.
But the seasonal cycle “entrains” this rhythm (cf. the idea of a zeitgeber). It offers a good way for everyone’s inconsistently-and-gradually-declining immunity to get below the threshold where an epidemic can start at the same time.
So in the tropics, Florida, and Alaska, epidemics “want” to follow a cycle of coming approximately once a year. In the tropics, nothing is giving them that cycle, so they come at a random time once a year, or twice a year, or whatever. In Florida, UV light, temperature, etc provide that cycle, and they come once a year. In Alaska, UV light, temperature, etc also provide that cycle, and they come once a year independent of what’s going on in Florida. It’s like the saying about how you don’t have to outrun the bear, you just have to outrun the other hikers. July in Alaska doesn’t have to outrun January in Florida, it just has to outrun January in Alaska, for the dubious honor of when Alaska’s destined-to-be-once-a-year flu season is going to be.
Zeitgebers
I think maybe they’re saying something like that getting a virus like this usually gives you about a year’s worth of immunity before your immune system “forgets” it. In retrospect, something like this has to be true: this sort of immune “forgetting” is why people keep saying we should get coronavirus booster shots.
So one possible model is something like: once you get a disease, you’re protected for a while. There’s no particular length of time, it’s a spectrum, absent any external rhythm-setter you would end up like the tropics, where people have epidemics at random times, once a year, twice a year, whatever.
But the seasonal cycle “entrains” this rhythm (cf. the idea of a zeitgeber). It offers a good way for everyone’s inconsistently-and-gradually-declining immunity to get below the threshold where an epidemic can start at the same time.
So in the tropics, Florida, and Alaska, epidemics “want” to follow a cycle of coming approximately once a year. In the tropics, nothing is giving them that cycle, so they come at a random time once a year, or twice a year, or whatever. In Florida, UV light, temperature, etc provide that cycle, and they come once a year. In Alaska, UV light, temperature, etc also provide that cycle, and they come once a year independent of what’s going on in Florida. It’s like the saying about how you don’t have to outrun the bear, you just have to outrun the other hikers. July in Alaska doesn’t have to outrun January in Florida, it just has to outrun January in Alaska, for the dubious honor of when Alaska’s destined-to-be-once-a-year flu season is going to be.
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