Re 1: Hardest hit would be the most helpful place to study. And I look forward to continued updates. The Stanford study, while there's certainly questions, has numbers in line with the Gangelt study. [1]

Re 2: Because much of the audience here is American, and there's not a similar study of the US population.

Re 3: No, the COVID-19 mortality rate is not 5.3%. The case fatality rate is 5.3%. Those are not the same, for an obvious reason -- currently the overwhelming majority of tests are carried out on people who go to hospital because they're sick. It's adverse selection bias.

For instance, it'd be like trying to measure the fatality rate of skydiving by measuring the odds that someone who ends up in the hospital with a skydiving injury dies. You'd think it's 99% fatal, but of course, it's not.

All you know is the numerator, not the denominator.

[1] https://www.stanforddaily.com/2020/04/17/santa-clara-county-...

That death rate is skewed. A COVID death is counted if the person had the infection and died, even if a co-morbidity would have killed them anyway. A person that has no symptoms or mild symptoms isn’t necessary known to have had the disease, which means there is a significantly lower death rate because the known infections is what’s used for the death rate, not the actual number of infections. A newly released study showed that 4% of Santa Clara County had exposure, but the “confirmed cases” is vastly lower than that. A 5% mortality rate is just false. Confirmed infections can’t be used to determine mortality because the number of actual infections is obviously going to be much higher. Mild or asymptomatic people aren’t going to the hospital to be tested so they aren’t being included in mortality calculations.

That doesn't matter much when there is no strong evidence that to have had COVID guarantees immunity[0] because being asymptomatic now doesn't mean they will be asymptomatic in the future, just South Korea has reported 116 people re-infected[0]

[0] https://www.telegraph.co.uk/news/2020/04/17/no-evidence-peop...

[1] https://www.aljazeera.com/news/2020/04/200413110301074.html

It's much more likely those in Korea received false negative test results earlier on. Let's say that was the case, though, 116 out of 2.5 million rounds to zero and is of no practical consequence to herd immunity or the potential effectiveness of a vaccine. All we need for either is 60-70% of people ending up with immunity -- so far your number is 0.0046%