They are distrusting of the government, pretty much. And usually they were convinced by some stats, that were probably made up about the government trying to poison people through vaccination.
Pretty much without exception I find the 'stats' which have been flagrantly fabricated come from one (of the many) entities who are focused on getting as many people as possible injected with as much as possible.
It's actually pretty interesting to see how the techniques of deception vary between the pro-vax entities. Some of them will give themselves a legal out when they lie, and some will just shamelessly make stuff up.
Generally speaking, government agencies in pharma companies will have something like '
we know of no studies have proven harmful effects', but they don't mention that any of the studies which have have been rejected on the basis that vaccines have no harmful effects and thus any study which shows them is automatically rejected as a valid study. They also don't mention that any studies which can show a negative effect are not funded by any entity but altruistic private ones, and any scientist who participates in such a study can kiss their career goodbye and will have to look for a new line of work.
Mainstream media, on the other hand is totally happy to make utterly absurd claims such as that the measles mortality rate at 50%, or claim that '
67 children died from measles in one hospital' when the official number for nation-wide mortality from the DOH isn't even that high.