That is not at all true. The majority of measles deaths are in children, as are chicken pox deaths.
It was not so long ago in our (US) history when more children died before the age of 5 than survived to their teen years. Author Roald Dahl wrote a heartrending account of losing his seven year old daughter to measles in 1962; he was never the same after this loss.
As for some vaccines not lasting, this is why boosters are given. The length of immunity induced by various vaccines is one component of the research that is conducted on vaccines, and is built into the recommended vaccine schedule.
About 5 years ago, I was tested for immunity against certain diseases. My medical record now says that I am medically exempt from having to have measles or rubella vaccines because I am immune. I was vaccinated against rubella in 1980 and against measles in 1984--thus, I am approaching 40 years of protection from those vaccines.
A relative’s wife and daughter died of polio in the early 60s.