I am old enough to have had all the standard childhood diseases (except whooping cough). Whether it is me having had them and building antibodies or someone younger who received the vaccine and building antibodies, a person is then immune. Measles, for example, does not mutate and become a different strain each year. Common Cold and Influenza are different strains, they mutate to something different each year. The previous flu shot generally does not provide protection for the new strain.

From what I understand, Covid-19 is not mutating. It is like the measles. Once you had it or got the vaccine, you are immune.