I am an autism researcher. While we cannot say 'vaccines never cause autism' we can say with confidence 'Other potential causes of autism have much better theoretical foundations, empirical evidence, prevalence, and effect sizes. With limited research budgets, we have better research targets to pursue first before further investigating vaccines."
When a layperson hears this, they'll think that there's a small but possible chance that vaccines do cause autism; when what the scientist means to say is that "it's highly unlikely that vaccines cause autism."