The son of a friend contracted measles even though fully vaccinated. He was among the few who did not respond with antibodies after being vaccinated.
Even though I was fully vaccinated against Hepatitis B, I never developed antibodies. I can get the disease just as easily as someone who has never been vaccinated.
This is why “herd Immunity” is so important in preventing epidemics.
Now that is a reasonable answer and you didn’t feel the need to ignore the hypothetical or pose a ridiculous non-sequitur straw man. Thank you!