As of writing:
- Italy has 827 deaths with 12462 confirmed cases.
- United States has 37 with 1302 confirmed cases.
- China 4600+ has deaths with 126000 confirmed cases.
- Germany has 3 deaths with 1966 confirmed cases.
- South Korea has 60 deaths out of 7755 confirmed cases.
These mortality rates by country are starkly different. Quality of healthcare in each country doesn't explain this. Percentage of elderly population by country probably doesn't. A different, more deadly strain might (though doesn't make a lot of sense with enormous differences in neighboring countries).
My best guess is that an enormous number of people throughout the world have already been infected. Probably many have recovered who never were identified in their medical system as having been possibly having contracted the virus.
There's a lot of reference to China's draconian quarantines being the reason for their drop off in new cases, but I think herd immunity might explain it. What I mean is, I think the virus was spreading wildly before it was contained. If you believe the R0 of 2+, then it could make sense.
Anecdotally, I know that not until 3/7/2020 (US time) did Shanghai start screening/quarantining international travelers into the country. 14 day mandatory quarantine, symptoms or not. So, through 3/6/2020 all travelers flying in were not screened. But Shanghai is running at a good pace now without exponentially growing cases.
Citations:
2020 coronavirus pandemic in Italy - Wikipedia
2020 coronavirus pandemic in the United States - Wikipedia
2020 coronavirus pandemic in Germany - Wikipedia2020 coronavirus pandemic in South Korea - Wikipedia
*Not sure why SK and China wiki pages aren't linking correctly, but a search should turn them up
**Also not trying to imply certain policy or protocol. Just wash your hands a lot with soap and water and don't touch your head. At least, that's what I've been told.