He emphasizes the cruise ship ( why ignore other whole countries?) and he distorts that example. Most never caught it: of those that did, all had excellent medical care. That’s no longer possible when many millions get infected – resources are limited.
He suggests a scenario in which 1% of the population gets infected and 0.3% of that 1% die. We are not seeing that low level of fatality in China, or Korea, or Italy. As for 1% getting infected, where the fuck does that come from? When a new pathogen shows up, no-one is immune, and the only limiting factor ( barring intelligent human action) is having enough contract it, recover, and develop immunity that the virus has trouble find vulnerable hosts. The limit, in a simple model, is when R0, multiplied by the fraction of never-infected people, is less than 1.0 . Since R0 is something like 3 ( assuming no major efforts at social distancing etc), that would require infection of 2/3ds of the population of the United States – with a death rate well above the 1% we’re seeing in places like South Korea. More like 4%, or even higher.
Again, where in the name of God does this 1% come from? Is Wuflu supposed to quit because he’s caught his limit?
The Faroe Islands had an epidemic of measles in 1846, investigated by Peter Panum, a young Danish doctor. There had been no measles in the Faeroes for 65 years – so only some elderly people were immune. Out of some 8000 inhabitants, how many ended up contracting measles? Was it 1%, due to some kind of viral gentility? 2%? 10%?
No: 6000 out of 8000 faroese got the measles, the kind of result you expect from a simple model. 75%. Measles has a high R0 ( ~10), which would have predicted 90% – but people over 65 had already had it, and even the Faroese don’t practice perfect panmixia.
The Spanish flu had an R0 around 2.0 . There had been an antigenically related flu around 1890, so older adults were less vulnerable. The percentage infected ranged up to 50% – which, against, is approximately the limit predicted by the value of R0.
When a pathogen is NOT novel, sure, you can have lower fractions of people vulnerable, because many people are already immune, and the fraction infected can be low. If it depends upon some regionally varying vector, like mosquitoes, sure, it doesn’t have to sweep across the whole country. If its R0 is only greater than 1.0 in some subpopulations, as was the case with HIV, it may spread only in those subpopulations.
But Wuflu IS novel, and does NOT depend upon a vector. The vulnerable subpopulation is those that breathe.
So, the surprise-free prediction is that it hits > 50% of the population –
Unless we stop it.