I rarely post here because no one will ever change their mind on anything, but you named 2 Islands and South Korea is a peninsula that borders North Korea where there is basically no interaction between the 2 countries.
We have lots of travel and immigration, legal and otherwise in America.
This is necessarily referring to neighbors sharing a land border, because if we're also counting immigration by air or sea, then it wouldn't matter if a given country is an island or not. So if we look at the countries that share land borders with the US - Canada and Mexico - both of them are doing better than we are. It doesn't make sense to blame them for our failures.
We are also the unhealthiest country in the world due to obesity, those are 2 big factors as to why we are worse than these 3 countries and probably a lot more.
I don't know that the US is "the unhealthiest country in the world" - there are many unhealthy countries that are a LOT poorer than us - but let's suppose that statement is true. If our population is
so much unhealthier than the rest of the world, shouldn't our federal, state, and local governments have been
the most restrictive in the world, in order to protect our much more vulnerable population? FL, in particular, seems like an extremely high risk given the older population of the state.