People used to line up for vaccines back when we first had massive distribution. The horrors of the diseases they prevented were so great the lines would go on for blocks.
People are insulated from those times. When those diseases don't seem so scary anymore, people start to worry about what they're getting injected with. Teaching people about how vaccines work seems to be one solution, but another one is a horrifying outbreak that shocks people.
The growing anti-vax movement is a danger to everyone, and they're a powder keg ready to explode.