“Herd immunity,” time consistency, and the epidemic yoyo

Saloni has long and detailed arguments against herd immunity.  Here is Caplan on Hanson.  Here is Kling on Hanson.  Here is the Taleb critique.  Here is the underlying Imperial College paper everyone is talking about.  The bottom line is that “locking everyone up to bend the hospital admissions curve” might have to last for at least a year to really choke off the coronavirus.

I’m not going to recap this complex debate, which most of you already have some inkling of.  Instead, I’d like to stress the issue of time consistency, noting that I’ll consider some extreme versions of policies to make exposition easier, even though no one advocates exactly those extreme versions.

Let’s say we expose lots of people to the virus rather quickly, to build up herd immunity.  Furthermore, we would let commerce and gdp continue to thrive.

Even if that were the very best policy on utilitarian grounds, it might not be time consistent.  Once the hospitals start looking like Lombardy, we don’t say “tough tiddlywinks, hail Jeremy Bentham!”  Instead we crumble like the complacent softies you always knew we were.  We institute quarantines and social distancing and shutdowns and end up with the worst of both worlds.

Alternatively, let’s say we start off being really strict with shutdowns, quarantines, and social distancing.  Super-strict, everything closed.  For how long can we tolerate the bankruptcies, the unemployment, and the cabin fever?  At what point do the small businesspeople, one way or another, violate the orders and resume some form of commercial activity?  What about “mitigation fatigue“?

Again, I fear we might switch course and, again, end up with the worst of both worlds.  We would take a big hit to gdp but not really stop the spread of the virus.

I also can imagine that we keep switching back and forth.  The epidemic yoyo.  Because in fact we find none of the scenarios tolerable.  Because they are not.

David Brooks postulates another possible form of time inconsistency:

What happens when there are a lot of people who’ve had the disease and become temporarily immune. They start socializing. Social distancing for the rest become harder if not impossible.


I greatly fear the epidemic yoyo.  And figuring out how to deal with it may be at least as important as calculating the numerical returns from various consistent policies.

I thank an anonymized correspondent for the term “epidemic yoyo.”


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