Age affects everything. The diamond princess cohort is much older than the population average. Older people are more likely to die from the disease, suffer symptoms from the disease, and catch the disease, all things being held equal.

The concept of death rates, symptomatic rates, and even transmission rates as a generic term is meaningless because it depends entirely on the age demographics of the population (and behavior, and other things, etc.).

The idea the most people who catch it are asymptomatic is true if our antibody tests aren't throwing out massive false positive rates. For something closer to the general population, the USS Theodore Roosevelt is probably a better guess.

https://en.wikipedia.org/wiki/COVID-19_pandemic_on_USS_Theod...

Looks like 90% of them had the disease on April 11. By April 20, 60% were asymptomatic. The last update seems to have been on April 22, with about 50% asymptomatic. That's probably a good bet for an actual figure in my opinion.

> Looks like 90% of them had the disease on April 11. By April 20, 60% were asymptomatic.

That's not what the wikipedia says... 94% of the crew has been tested for Covid, with 678 positives. Infection rate ~15%.

From those infected, ~60% didn't show symptoms.

That's correct, my mistake on the infection rate of 90%. The 60% on the wiki figure is coming from an article written April 16. I did a bit of digging and found a navy statement from the 22nd which said 50%.

However given my error on the 90%, it seems much more likely that a large proportion of the people asymptomatic on the 22nd had caught it more recently than I was assuming, so the asymptomatic rate is probably a bit worse.

I would assume the crew of a military ship are substantially younger and healthier than the general population. Since both health and age seem to play a key role, 50% is almost certainly an upper bound, with the true number lying between 17% and 50%

Most will be in the range of 20-40. Some will be older, but none will be kids. So take it as you will. The true number doesn't have any intuitive meaning anyway, since the likelihood of being infected is correlated with the likelihood of being symptomatic.

E.g. if hypothetically people under 20 never exhibit symptoms but also never get the disease, they won't bring the asymptomatic rate down because they won't be infected in the first place.

Averages suck in this context.

There are indications that severity of infection is proportional to the initial viral load. I'd imagine that being locked in close quarters on a warship would subject the sailors to a higher viral load than you'd expect in the general population, and subsequently they'd have on average more severe infections, so it could be lower than 50%.