[Mr Inviso]

you’re wrong, though. Having had chickenpox is not necessarily protection against having it again (shingles) as an adult. A fact that I can attest to personally.

I do understand spreading out the vaccines, though. That makes real sense.

[Dr. Sivana]

Having had chickenpox is not necessarily protection against having it again (shingles) as an adult.

I am sorry that you had to endure shingles. You're right, as you know. Interestingly, (according to Wikipedia)

"In the United Kingdom and other parts of Europe, population-based immunization is not practiced. The rationale is that until the entire population could be immunized, adults who have previously contracted VZV would derive benefit from occasional exposure to VZV (from children), which serves as a booster to their immunity to the virus and may reduce the risk of shingles later on in life"

So, you're right, there is no guarantee. It still is reasonable to allow some exposure.