Going to take a stab at explaining what this might mean, and why it matters. https://twitter.com/paulbohm/status/1252977663796371458

So basically, there's been a lot of discussion of whether covid produces a lot of asymptomatic cases.

If it does, good! Fewer people get sick. Also, asymptomatic cases are less likely to be detected, because people who don't feel sick don't get tested.

Which would mean that covid is less fatal than it looks if you just look at deaths divided by reported cases. So the more cases are asymptomatic, the better.

Hence lockdown skeptics tend to fixate on very high, very implausible estimates--80-99%. There's no evidence for that.

There's a rough consensus, based on whole-population studies or random samples, that 25-50% of cases are asymptomatic.

Diamond Princess cruise ship, where they tested the whole population of passengers, was one of the earliest studies; in March reports were 46% asymptomatic.

So what this study did was take some CT scans of 100 mostly asymptomatic covid patients from the Diamond Princess--roughly 3/4 were asymptomatic.

And on the scane roughly half of the asymptomatic had the classic "Ground glass" lower lungs that are characteristic of covid.

If this generalizes--and of course it's a study of 100 people who aren't a representative population, so it might not--then what this is telling us is that whatever you think the asymptomatic rate is, cut it in half.

You might wonder how people could have lungs so messed up that you can see it on a CT scan, yet feel fine. And now we enter one of the mysteries of covid: it often looks less like a classic pneumonia than severe altitude sickness.

Doctors have been puzzling over this for a while and they're starting to think they know why: until covid is pretty severe, it affects your lung's ability to process oxygen, but *not* to expel carbon dioxide. And accumulating carbon dioxide is what makes you feel breathless.

So basically, if this result holds, people were actually pretty sick, but they just didn't know it. And that means they might have sustained serious damage, again, without knowing it.

There are some disturbing reports from Austria of just this: people with mild cases and real bad lungs. https://www.rainews.it/tgr/tagesschau/articoli/2020/04/tag-Coronavirus-Lungeschaden-Forschung-Uniklinik-Innsbruck-6708e11e-28dc-4843-a760-e7f926ace61c.html?fbclid=IwAR3nNrZcHfJyuilDzk3yzvb3ySqmZ6I7ON_EtWQVmtWEGBTnI8jkgtyrRrY

Also stories like this: young people, mild cases or no symptoms, suddenly showing up at the ER with strokes. https://www.cnn.com/us/live-news/us-coronavirus-update-04-22-20/h_d7714f05dc8e434921f5b48ecce4484b

The Washington Post, of course, did an excellent, and terrifying, article on some of these other complications yesterday: there appears to be a clotting component to this too. Hence the strokes. https://www.washingtonpost.com/health/2020/04/22/coronavirus-blood-clots/

All of which point to a really scary, and far-too-plausible possibility: that rather than being milder than the lockdown advocates were suggesting, this disease might be way worse than we we thought.