I talk a lot about the mistake people make thinking it is always safer to err on the side of extreme action.

Here is a simple thought experiment to illustrate this point.

Imagine you are given a magic wand which, if you wave it, will reduce COVID transmission by... 1/11

90% for 2 weeks. The magic wand has no side effects, and it can only be used today.

Should you wave it?

It doesn't sound like a hard question. The magic wand only confers benefits, it seems, and no costs. What could be the problem?

Surprisingly, in some situations... 2/11

waving the magic wand can result in more COVID mortality and morbidity than not waving it.

The reason is that even in the simplest epidemic models, where all individuals are identical, the final size of an epidemic is not monotone with respect to a time-varying pattern... 3/11

of transmission. That is, if transmission rates will be constant forever, then yes, the lower transmission rate, the smaller an epidemic you'll have. But if they will vary over time (e.g., with the seasons), then reducing transmission rates (especially just for a limited period)

can actually backfire, leading to a larger second wave and a larger total epidemic.

Things are even more counter-intuitive in more realistic situations, where populations are highly heterogeneous.

For example, suppose now that you are given two magic wands: 5/11

one wand just temporarily reduces all transmission involving people above 50, and the other just temporarily reduces all transmission involving people below 50.

What we showed in our paper with @ChikinaLab is that in this situation... 6/11

you can do better by throwing the first wand in the trash and just waving the second one.

(Please note, however the importance of actually reducing transmission involving older individuals in this scenario.) 7/11 https://twitter.com/WesPegden/status/1288140129677332482

There are all sorts of tricky questions posed by the nonmonotonicity of epidemics.

For example, is COVID more deadly in winter?

https://twitter.com/WesPegden/status/1294739254485057539

If so, we should be probably be very careful about waving "summer" wands, but we may be likely to wave any "winter"... 8/11

wands we can get our hands on.

Navigating the counterintuitive consequences of this for COVID response requires gathering and examining evidence, making decisions in the face of imperfect information, and level-headed scientific discussions motivated by a search for the truth,9/

rather than by a desire to support whatever policies we were advocating for back in March.

Unfortunately, policy cheerleading still seems to be diving much of the scientific discourse at this point, which is leading us to ignore important questions... 10/11

(like seriously, is COVID more deadly in winter?) whose answers would help us choose policies which could lead to far less death and suffering then we will face by following our first guesses.
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