Anyone entering most West African countries must have proof of a Yellow Fever vaccination. One used to have to have a booster, but now a single jab lasts for life.
One cannot enter the countries there without this proof (It's like a small passport)
Also, one needs proof of being free from TB, and a fairly recent X-ray document is required.
I think the time will come when one will need similar proof of a Covid vaccination to be allowed to fly, book into a hotel, even enter a restaurant or bar etc. Abroad and probably here at home too.