I'm sure some people are mistaken and think Trump himself is anti-vaccine, but most people (that I am aware of) that put some measure of responsibility on him do so not because of his specific stance on it, but for his part in the flywheel that created the current political climate.

He has been closely in bed with the sections of media that have pushed the narrative, generally celebrated paranoia towards experts, and consistently pushed the idea that you can't trust the government. If you lose control of the bolder you helped push onto the slope, it doesn't mean that you don't have responsibility in pushing it to begin with.

He has given credence to the vaccine-autism link early in the 2016 debates and in tweets.

He was also instrumental in pushing early treatments that didn't pan out as hoped. These often became the subject of conspiracy theories about a whole slew of medical professionals avoiding real treatment, and the pandemic being some authoritarian plot. Trump was there sowing doubt in medical professionals. He may have encouraged vaccination itself, but his actions on the whole produced distrust so that there is a pronounced deficit of vaccination in his electorate.