The coronavirus is here to stay — here’s what that means
That article seems comprehensive.
It will take a few yrs to figure out, if there is a time limit for immunity. Especially for the 65+ crowd as new variants arise.
Only thing missed in the article is that not only did Flu A originate from birds, but every year the epidemiologists can trace the virus recombination in migrating birds from HK to Australia and back. Allowing a guess as to what the next yr's variety will look like.