There are altogether too many people who never lived through the times before vaccines for childhood diseases.
I remember a polio outbreak in school about a year or two before the Salk vaccine; my parents kept us home for 2 weeks. Two of my classmates wound up with paralysis and confined to wheelchairs.
People today have never seen whooping cough, measles, rubella, and so many other diseases. The are protected, spoiled and full of themselves.
Not even doctors have seen all those. My youngest son developed a rash that looked like measles to me. My older kids had had it, but none of my younger ones had. The doctor I saw to confirm measles (my son had other health issues, so I needed to know) admitted she had never seen measles in real life. It took another two doctors to decide it was in fact measles.
You're right. They take their good health for granted even though it's largely because others had the common sense to be vaccinated. I was born just after the discovery of the polio vaccine, but I remember well the epidemics of measles, mumps, whooping cough and chicken pox that swept through our family.
My poor Dad caught the mumps from us when he was 40. He'd somehow missed it as a child. He told us they were too poor during the Depression to have mumps.