Simple people do not like it when things get turned upside down. It affects them figuratively at a molecular level. In many cases it's not that they have an opinion of vaccines, it's just that the first person who brought it up told them that vaccines are dangerous. So that is what they believe. They're many people who think like this and will never change their minds until conditions are right, if ever.
Kids are famous for this, remember pluto. Their teachers told them that pluto is a planet and that is what they'll automatically believe. So when pluto was demoted, kids felt betrayed for what their teachers told them was a wrong. Almost as if they lied to them. Who can blame them, you get punished for being wrong in school.
Same thing goes for everything. People like things when it benefits them and hate things when it takes something from them. Even if that something only exits inside of their minds.