Well, I live in Japan and went out properly today for the first time in days, and I can tell you that the R0 is above 1 by eye simply by the way people are behaving.
Social distancing isn't happening much at all, and unless the population is magically becoming immune then there's no way R0 is less than 1. The real questions are whether that will translate into symptomatic and serious cases, and when.
But there isn't a big spike in pneumonia/ER/ICU numbers either. So it's supposedly not a case of high undetected number of infected running around, laying in hospitals, and it doesn't seem like the government is trying to downplay it either, even if their testing protocol is not extensive enough. (Though they are of course incentivized due to the Summer Olympics.)
Considering the physical proximity of Japan and China (30% of tourists to Japan are Chinese) the fact that Japanese hospitals haven’t been overwhelmed like Italy suggests the virus is not spreading as rapidly there. (Testing may also be a concern but lack of testing cannot hide overwhelmed hospitals).
But why? I have pushed my air quality hypothesis. What other reasons are there.
And you can't just claim social distancing. Unless they have shut down their trains, where people are literally packed in, that just doesn't fly. (So, have they?)
There are a number of thoughts I have, but I'm puzzled as well. My first explanation is that the Japanese are simply more hyegeinic than most other countries I've been to. Fastidious is the word that comes to mind. They wash hands often, wear clean clothes, wear masks or stay home when sick, don't shake hands or touch often.
Second explanation that comes to mind is that they tend to be just healthier than other countries. They have low obesity, exercise correctly and routinely, walk and ride bikes to get where they go, and do all of this even when elderly. The counterpoint to this is that they have a really high smoking population.
The first one could explain why it isn't spreading there. Without testing, hard to know if that is accurate. Reports from other threads supports that it is there, but not severe cases. (Sadly, anecdotes...)
Second is also tougher to square. The risk pool is supposedly older people, per reports from Italy. But, that doesn't seem to square with age profiles of Japanese. So??
One difference could be that old people in Japan are all too often living a solitary existence or not in frequent touch with their family. My wife brought this up last night as I was discussing this thread with her and out of everything I've seen, read, and considered, this seems to be the one thing that could stop it - they were already socially distancing the most vulnerable group.
The virus has been in Italy for a lot longer than they think, and they get close to each other/have actual contact a lot (I don't know if that's actually true, I've never been to Italy)
Maybe they mostly have a particular mutation that is more deadly/infectious
Don't discount the possibility that figures are being massaged in various ways. One is the obvious lack of widespread testing. Another is the reports of people with symptoms being turned away. Then there are the kodokushi[0] numbers which are a clue to how the government already deals with uncomfortable mortality figures - let alone those kudokushi who may die because of the virus - and a over a million deaths a year (I don't know the monthly totals) in which to hide a few hundred (initially) deaths, especially while still in flu season.
In short, I trust the figures here about one step more than ones coming out of China.
I can't square that it has been in Italy substantially longer than Japan. Nor that Italians touch each other more than Japanese. Have you ever seen the videos of commuter trains in Japan?
So, possible, but seems not as likely to be the explanation.
Social distancing isn't happening much at all, and unless the population is magically becoming immune then there's no way R0 is less than 1. The real questions are whether that will translate into symptomatic and serious cases, and when.