Or maybe people believing the anti-vaxxer hype instead of reality. In every vaccine there has been a very tiny percentage that have had a negative reaction to it. It is to be expected that in a few people the introduction of a foreign substance will cause an immune overreaction. No different with vaccines and much less common than anaphylactic shock from bee stings.

People today are no less gullible then they were in the past. Where the difference lies today is the speed of transmission of information that anti-vaxxers (or any conspiracy theorists) can use to spread their lies and the breadth of information they can drop to reinforce them.

Those at the top of the conspiracy theory food chain gain money and power. Those at the bottom are reinforced in their delusional beliefs by the feeling of having special knowledge and being smarter than the non-believers. That endorphin boosting feeling of importance is so strong that fact and logic are thrown out the window.