To be fair, the mortality rate could be a lot higher than estimated. That has huge error bars too. We all look on the bright side (why it might be lower). There's also a dark side.
Based on what? Nothing points to a higher mortality rate - but some countries are admittedly not testing a lot. Even if you quadruple the estimated mortality rate, the UK numbers would still be under-represented.
The virus takes a while to run its course. We don't know how many people die in the end. There's a huge number of people who have neither recovered not died yet. A lot of people focus on Diamond Princess, which was at <1% fatality late March. It's already up to 1.6% (the 12th passenger just died). 82 are still sick, of whom 9 are in severe condition. That's one of the first set of cases, so that's a lower bound with perfect medical care. Those 9 who are still in sever condition will almost certainly have permanent lung scarring. I'm not sure the status on the 82, but they've sick a long, long time -- we're now something like two months in.
Lower bound: Deaths/(total cases)
Upper bound: Deaths/(deaths + recovered)
Some media in France tend to focus on the upper bound, and reports numbers in the 10-30% range, so the country is very open to very severe measures. The US tends to be optimistic, and everyone plays it down, so the virus is spreading like wildfire.
On the other hand, I don't think "perfect medical care" is an accurate description of being quarantined on a boat with limited diagnostics and an illness your doctors have never seen before, and I also think the cruisegoing cohort skews much, much older than a general population.
Of course. As I said, you can try to paint a pretty picture, or an ugly picture. We don't know mortality rate very well yet (or much of anything else). Ever estimate has huge error bars in both directions, and the scientific estimates are sort of a median.
People in the US tend to look for every silver lining, preliminary study showing a potential breakthrough, and any reason it might not be so bad. That's a bias which has led to this not being taken seriously enough at any point.
I kind of treat the WHO estimates (1% with ventilator, 6% without, and 3.5% median) as just that: best-available estimates. It might be much, much worse. It might be much, much better.
