I understand that about vaxxes. Specific to the flu virus, the reason for annual flu shots is that particular virus is constantly mutating, so even if last year's jab confers lifetime immunity, it will only be against that strain.
But regarding having been infected and the "immunity" it confers, from what I have read on the subject, the anti-body count deteriorates rapidly. This has led to numerous cases of the fully vaxxed post-infection, still succumbing to a second attack.
Fortunately, there are some vaxxes which do confer life-time immunity such as Small Pox and Polio, but there is yet to be one that can do so with any of the Coronaviruses.
I hope you don't think I am Yank bashing. The US has done a lot of good, but a lot of that good has been undone because a huge chunk of America is in an undeclared war with itself. That became obvious when you could see Americans abusing their fellow countrymen for the crime of wearing a mask.
My concern, is that while Americans are fighting a proxy war with the virus as an underlying factor, the virus is going to be around for a hell of a long time. I've seen those that say "People are not dying from the virus, but from underlying conditions". That's mainly true, but there are those who are young and healthy who it does kill. More to the point though, if you just count the obese, diabetics and asthmatics, there are over 200 mill cases of these in the US. In fairness many of those will have more than one of those conditions, but these are among the most common health conditions in the US, and I'd guess that the total number with at least one of these conditions numbers150 mill.
Now factor in that the vaxxes, although better than nothing, are not perfect. They don't guarantee immunity, and for those with immunity because of vaxxing, that does not prevent them being carriers. As I've said, I estimate that maybe as many as 30% will refuse the vax. I hope I am wrong. But if I was deciding which countries to open up to tomorrow, I'd be looking at the US and the metrics and saying that "Proportionately. they have 4X more infections than average, 3.5X and 10X more unresolved cases than average. 30% are refusing to get vaxxed, and many are not only refusing to wear a mask, but abusing those who do. Do I really want to let them into my country and risk the recent gains we have made"?