https://astralcodexten.substack.com/p/long-covid-much-more-than-you-wanted

Like everyone else, I'm trying to figure out how cautious I should be around COVID. It seems like the most important concern for young vaccinated people like myself is the risk of Long COVID symptoms, so I spent a while trying to figure out what those were.

My basic conclusion is that everyone else is right, that news stories on this phenomenon seem remarkably good, and that there's not much we know for sure beyond the simple summary you've probably already heard. Insofar as anything surprised me, it was how bad the worst-case scenario would be.

Here are some of the basic things I found:

1. Long COVID is probably a lot of different things, some of which are boring and obvious, others of which are still kind of mysterious.

First, people with severe COVID that lands them in the ICU have long-lasting symptoms in multiple organ systems. This isn't surprising, and should be considered in the context of post-ICU syndrome. Basically, if anything makes you sick enough to land in the ICU, your body is going to be pretty scarred by the illness (and maybe also by the inevitable side effects of intensive care), and this will last a long time and cause many problems. EG if you're bedridden for many weeks, your muscles waste away, and then it takes a long time for them to recover and you feel weak and fragile until you do. Or if your lungs stop working and you need mechanical ventilation, your lungs might be pretty weak for a while, and other parts of your body might not get quite the amount of oxygen they're used to and might get damaged in a way that takes a long time to recover. There's a similar problem where if you are sufficiently old and frail, any illness will take you down a level of functioning and you might not be able to get up a level again. See for example this article discussing how about 1/5 of elderly flu patients have "persistent functional decline" and may never regain their pre-flu level of functioning.

Second, even in young people with milder cases, COVID can sometimes cause lung damage. If you get lung damage, you'll have at least breathing problems, and maybe other problems. Your lungs will probably heal eventually, but some kinds of lung healing cause permanent scarring; this can present as shortness of breath on exertion, or become a problem later after other lung injuries.