I think there are a number of factors at play here: - Many people believe their social network over authoritative sources. - There is a general (and many time

I think there are a number of factors at play here: - Many people believe their social network over authoritative sources. - There is a general (and many times legitimate) distrust of "Big Pharma", especially in the US. - Protecting children triggers a deep emotional instinct in parents. This provides a strong motivator for people to do research into what substances are being put in their childs bodies. - Autism is scary for many, in part because its not currently well-understood, nor are its causes. Anti-vaxxers capitalize on this fear to present causal arguments in absence of an authoriative science-based one. People who need answers will find one, one way or another. - Reported cases of autism are on the rise, this is a generally-accepted fact. This is most likely due to our improved understanding of what autism is of course, and not due to the rise of vaccines. We can shout "Correlation != Causation" all we want, but at the end of the day, scientific education is quite poor all over the world (especially in the US where its actively demeaned by many groups, whether for financial, ideological, or religious reasons), and a lot of people quite simply just don't think this way. We are hard-wired to find patterns in the world, and the world is complex - many people will quite simply find the wrong ones. - Anti-vax is partially due to the success of vaccines, people of parenting age today were born into a world without polio, measles, smallpox, etc. This may lead people to believe the vaccine "didn't do anything" (which is kind of the point!). Preventative measures (vaccines) don't have the same response as reactive measures (cures), we're just not hard-wired for it emotionally. - There exist a number of sources online that imply vaccines cause more harm than good. This is the first google result I found when searching "number of vaccines in usa", a realistic search term a concerned parent might use: https://www.fourteenstudies.org/nowwhat.html https://www.fourteenstudies.org/nowwhat.html These present a number of studies that appear to show a link between vaccines and autism. As I sit here, I could not refute each study one-by-one, and other than the goofy styles, I could not articulate to an anti-vax parent, or even an undecided one, why these are bad science. In fact, it doesn't even seem like an unreasonable hypothesis to me that "Big Pharma" is pushing vaccines of dubious necessity for profits - the incentive is clearly there. So its not as illogical as it might seem - Fixing these attitudes is a difficult problem, and not one with an easy solution. We can start by improving scientific education, and improving the way that institutionalized knowledge is distributed. We need to somehow figure out how to collectively "remember" why these vaccines are necessary in the first place, well after the people affected by these diseases in the past are gone.