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I've written a blog post on "Body Mass and Risk from COVID-19 and Influenza", available at https://radfordneal.wordpress.com/2020/04/06/body-mass-and-risk-from-covid-19-and-influenza/

Here's the intro:

Understanding the factors affecting whether someone infected with COVID-19 will become seriously ill is important for treatment of patients, for forecasting and planning, and — with factors that can be changed — for personal decisions aimed at reducing risk. Despite our current focus, influenza also remains a serious disease, so understanding its risk factors is also important.

Here, I’ll look at some of the evidence on how body mass — formalized as Body Mass Index (BMI, weight in kilograms divided by squared height in metres) — influences prognosis for respiratory diseases. Information specific to COVID-19 is still scant, but there is more data on influenza and on other respiratory infections (which includes coronaviruses other than COVID-19). Information on how BMI relates to general mortality should also be helpful.

Below, I’ll look at two relevant papers, plus a preliminary report on COVID-19. To preview my conclusions, it seems that being underweight and being seriously obese are both risk factors for serious respiratory illness. Furthermore, it seems that “underweight” should include the lower part of the “normal weight” category as defined by the WHO. Official advice in this respect seems dangerously misleading.

Thanks so much for your help!

I'm curious why you don't expect this to bounce back when the pandemic or recession is over?

Fixed, thank you.

I have heard anecdotal evidence that this has happened, but the only official numbers I can find are of the early Wuhan study. Does someone have a better sense of whether or not this has happened?

Yeah, that is one of my favorite videos by 3Blue1Brown and more like it would be pretty good.

This is fantastic. Can I encourage you to make it a top level post?

Fixed the image. The problem was that you used a link the page where imgur embeds the image, and not an actual link to the image itself. To get the image link, right-click on the image and click "Copy Image Address". 

I would also like to investigate this question for MERS, SARS, the 1968 Hong Kong flu, and (as far as it's relevant) the 1918 Spanish flu.

I'd be very interested in analyses of those (esp. if you look at it from the limited perspective people had in the early stages of those outbreaks). I feel like I completely missed it at the time, but the more I hear about SARS-1 the more I feel like the alarm bells should have gone off like crazy (and that probably happened in Asia but the way I remember it, reporting on SARS in the West felt no different from reporting about bird flu or Swine flu – but probably I didn't play close attention because I was really young).

>The death rate from swine flu was 0.02%, hitting the young harder than the elderly. I count this as a no.

This is not quite the right way of looking at it! I think you'd have to look into what experts thought during the early months of the Swine flu outbreak. I haven't researched this but I've read that early best estimates for Swine flu fatality were at least a factor of 5 higher than the true infection fatality rate, if not even higher. (The IMO misguded folks who think the IFR for Sars-CoV-2 could be as low as the flu's are constantly pointing this out, failing to flag that this is far from a universal trend among outbreaks – e.g., early estimates of Sars-1 fatality turned out to be underestimates.)

That said, it seems plausible that even with my proposed adjustment, the numbers would still remain below the thresholds you list under "harm." It depends on how much credence experts put on the higher end of the range during the early months of the Swine flu outbreak. I don't know just how high the highest estimates were that still came from credible experts.