Tl;dr long-term fatigue and mortality from other pneumonias make this look very roughly 2x as bad to me as the mortality-alone estimates.
It’s less precise than looking at CoVs specifically, but we can look at long-term effects just from pneumonia.
This 10-year study on young children shows 10+/-3% sequelae involving restrictive lung disease, obstructive lung disease, or bronchiectasis. In the absence of a control group, they noted that hospitalized vs non-hospitalized cases showed the expected discrepancy of 5+/-2% sequelae and 14+/-7% sequelae. Apparently adenovirus cases had 55+/-8% risk of sequelae though, and those small error bars do make me wonder if there were enough adenovirus patients to shift the sequelae rates up significantly in the whole population. (Extrapolating from the SDs would give about 40⁄200 people in the adenovirus group, which would exactly make up the whole effect, but actually n=720, not 200, so I’m obviously doing something wrong.)
This pretty interesting study took people hospitalized for pneumonia and “non-pneumonia” and looked at mortality rates between them. The pneumonia patients had about twice the mortality over the following 1 year and 5 years, but by the 5 to 9 year range this had dropped to 1.5x and by 10+ years it was only 1.25x. The absolute mortalities were about 1.25% in pneumonia patients over the first year excluding the 30 days following the disease, down to about .5% during years 5-9, so for the average person this adds up to about 4% increased mortality over the next decade (so about 6% → 10%). Notably, COD was only 12% respiratory but 24% neoplasm and 36% circulatory system. One difficulty in this study was that there was somewhat higher comorbidity in pneumonia-havers, though scrapping anyone with comorbidities (including age) still left young people at a 2.4 hazard ratio (and the elderly only showed a 1.4 hazard ratio).
As far as fatigue goes, obviously numbers are very difficult due to lack of measurement, but this study says bodily functioning is still on average about 5% worse at 3 months, and a site reporting on it says it claimed 50% of people still feel fatigue after 3 months (but I couldn’t find that number in <3 minutes). Another study says only 63% of people are symptom-free at 6 months. Likewise, this site says at 3 months “most symptoms should have resolved, but you may still have fatigue”, and says at 6 months “most people will feel back to normal”, but that sure sounds like it easily includes the possibility of 20% fatigue at 6 months and 10% at 5 years.
this research has made me pretty concerned about lasting symptoms. Just to be fatigued for 6 months sounds horrible, and to have even a few percent chance of that forever would rival my concern over the mortality. Additional long-term increased mortality and lung problems might add up to a similar order of magnitude.
The one redeeming piece is that pneumonia is actually quite bad (5-10% mortality), so COVID might actually be less extreme than these numbers. One could take these pneumonia effect numbers and reduce them by 3 to fit 1.5-3% mortality, but since the 20% who do get pneumonia appear to have like 20% mortality, that makes the pneumonia seem worse and thus plausible to have adenovirus-pneumonia-like high rates of long-term side effects, which would move COVID back toward about the middle of the pack.
The second study has a classic ‘adjusting for observed confounders’ methodology which comes with classic limitations such as that you don’t observe all confounders. For example, they control for alcohol, drug abuse, but not smoking (!)
The first study also acknowledges possible confounding but I haven’t checked it in detail.