Here are some ideas I brainstormed fairly quickly:
I see no signs of researcher misconduct, but I don’t see enough evidence to be very confident that their evidence is real.
Could people in Japan be much healthier to start with than most of the countries that have an IFR > 0.1%?
what are Japanese vitamin D levels?
I suspect they have high vitamin K2 levels (from natto, kimchi, etc.). What does this do?
less obesity?
different genes (blood type? fewer APOE4 alleles?)
Could transmission there involve a much lower initial viral load?
Could they do an unusually good job of preventing transmission to vulnerable people, while enabling plenty of transmission between others?
The only research I found time to do was to check the vitamin D content of fish. I was mildly surprised to find that it’s high enough to make vitamin D deficiency fairly rare in a culture that expects virtually everyone to eat fish.
I’ll give a 25% chance that vitamin D explains more than half of this puzzle. Most of the other ideas are quite unlikely to explain more than 5% each.
If that study’s seropositivity rate generalises to the whole of Tokyo then there have been ~4,300,000 actual cases.
Japan’s positivity rate on testing during the second peak got up to 6% so it is unlikely they are missing that many cases.
The numbers are so far apart that I wouldn’t really believe that the seropositivity rate generalises at all.
(Note that Tokyo has 400 confirmed deaths and 25,000 cases giving CFR = 1.6%. Assuming some missed cases this puts the IFR in the normal range.)
Looking at it in a bit more detail the seroprevalence increased before Tokyo started seeing increases in positive tests so I really don’t think these numbers will pan out in the long run.
EDIT: actually 25k is Tokyo prefecture and 4.3M refers to Tokyo city—Tokyo prefecture at 46.8% would be 6.5M.
The Japanese study is pretty weird.
Here are some ideas I brainstormed fairly quickly:
I see no signs of researcher misconduct, but I don’t see enough evidence to be very confident that their evidence is real.
Could people in Japan be much healthier to start with than most of the countries that have an IFR > 0.1%?
what are Japanese vitamin D levels?
I suspect they have high vitamin K2 levels (from natto, kimchi, etc.). What does this do?
less obesity?
different genes (blood type? fewer APOE4 alleles?)
Could transmission there involve a much lower initial viral load?
Could they do an unusually good job of preventing transmission to vulnerable people, while enabling plenty of transmission between others?
The only research I found time to do was to check the vitamin D content of fish. I was mildly surprised to find that it’s high enough to make vitamin D deficiency fairly rare in a culture that expects virtually everyone to eat fish.
I’ll give a 25% chance that vitamin D explains more than half of this puzzle. Most of the other ideas are quite unlikely to explain more than 5% each.
I suspect that those results don’t generalise to the whole population.
Japan’s testing shows 25,000 cases in Tokyo.
If that study’s seropositivity rate generalises to the whole of Tokyo then there have been ~4,300,000 actual cases.
Japan’s positivity rate on testing during the second peak got up to 6% so it is unlikely they are missing that many cases.
The numbers are so far apart that I wouldn’t really believe that the seropositivity rate generalises at all.
(Note that Tokyo has 400 confirmed deaths and 25,000 cases giving CFR = 1.6%. Assuming some missed cases this puts the IFR in the normal range.)
Looking at it in a bit more detail the seroprevalence increased before Tokyo started seeing increases in positive tests so I really don’t think these numbers will pan out in the long run.
EDIT: actually 25k is Tokyo prefecture and 4.3M refers to Tokyo city—Tokyo prefecture at 46.8% would be 6.5M.