For me personally the unknowns of such a new virus mean that the existence of the case studies would be enough to be concerned. And the strongest case is made by the fact that this virus' closest relative known to infect humans has caused lasting damage to people with cases that lead to hospitalization:
"Evidence from people infected with other coronaviruses suggests that the damage will linger for some. A study published in February recorded long-term lung harm from SARS, which is caused by SARS-CoV-1. Between 2003 and 2018, Peixun Zhang at Peking University People’s Hospital in Beijing and his colleagues tracked the health of 71 people who had been hospitalized with SARS. Even after 15 years, 4.6% still had visible lesions on their lungs, and 38% had reduced diffusion capacity, meaning that their lungs were poor at transferring oxygen into the blood and removing carbon dioxide from it."
We know this much and SARS is poorly studied because it faded away so we generally lost interest in it. This virus is both similar and different enough to be very, very wide spread so even minor negative effects over the total population that gets moderate to mild cases will have the potential to have very large impacts on worldwide health.
As time goes on we are going to better document the consequences of mild and moderate cases and understand these things better, caution seems advisable until we do.
It's important to remember that SARS was a lot more deadly that COVID-19. I am not at all surprised such a high percentage of people suffered long term lung damage given how virulent it was. Case fatality was somewhere around 10%.
I'm curious if there was widespread serology testing to get to that number with the original SARS. That's in the ballpark of what the early SARS-COV-2 research (15%) showed until we realized there were asymptomatics and people who don't go to the hospital (because they aren't severe) and that numbers drawn from the hospitalized were not representative. If that number was just pulled from hospitalizations because we shut SARS down before we studied it as closely, it makes me wonder if the mortality rates are similar.
There was not widespread serology testing but subsequent analysis has the WHO pegging the fatality rate at about 3% (as opposed to the 10% from the time of the outbreak itself).
We didn't really shut SARS down so much as it seemed to have shut itself down, conventional epidemic control measures were enough to contain it and it was not quite easily transmissible enough to sustain itself in the wider population without being allowed to gain a real foothold undetected first.
That last point would be why you would not expect (and I would think it is impossible) to find that at the end of the day COVID-19 will be anywhere near as deadly as SARS. We have strong evidence that it takes truly extraordinary measures to suppress this new virus at a rate that will in fact eliminate it from a population when compared to SARS. SARS simply didn't spread that widely because if it did that would directly contradict the relative ease of its containment.
Sounds like they're saying Coronaviruses aren't a new thing, just that new types pop up. The CDC lists human Coronaviruses were first found in the mid-1960s [0]
Ok, how is that relevant?
Coronaviruses collectively have been known for a long time, this was also true when the SARS outbreak occurred, is true during MERS.
Likewise influenza was well known before the 1917 pandemic, or H1N1.. and?
https://www.nature.com/articles/d41586-020-02598-6
"Evidence from people infected with other coronaviruses suggests that the damage will linger for some. A study published in February recorded long-term lung harm from SARS, which is caused by SARS-CoV-1. Between 2003 and 2018, Peixun Zhang at Peking University People’s Hospital in Beijing and his colleagues tracked the health of 71 people who had been hospitalized with SARS. Even after 15 years, 4.6% still had visible lesions on their lungs, and 38% had reduced diffusion capacity, meaning that their lungs were poor at transferring oxygen into the blood and removing carbon dioxide from it."
We know this much and SARS is poorly studied because it faded away so we generally lost interest in it. This virus is both similar and different enough to be very, very wide spread so even minor negative effects over the total population that gets moderate to mild cases will have the potential to have very large impacts on worldwide health.
As time goes on we are going to better document the consequences of mild and moderate cases and understand these things better, caution seems advisable until we do.