Take a look at my post above. The group in perspective is not the ones who did well even without vaccination. But focus on the group that was actually saved by them. I will give you the example once again. If 1000 children are receiving Polio vaccination and 2 of them were exposed to polio virus later in life. Here whats important is the 2 children that were saved due to the vaccination, not the rest 998 who wasnt effected. So if 2 out of every 1000 is benefited with vaccination. Imagine how many lives will be saved while vaccinating millions of children. Do the math.