The problem with understanding things from their fundamentals is that it doesn't scale. The world is too complex.
Are vaccines safe? Maybe I'll just should read through the Institute of Medicine's definitive, 900 page "Adverse Effects of Vaccines: Evidence and Causality."
Can these robust explanations be simplified for lay people? Yes, but faced with competing, simplified explanations, can lay people dependably evaluate which is correct? Can they do it better than a domain expert?
I have some understanding of how vaccines work, from school and popular science literature. But if tomorrow leaders in the field of medicine broadly announced that all of our understanding of vaccines up until now had been mistaken and that there was now some new explanation, well I would accept that new explanation. Whatever education I have had on the topic, it is obviously not going to be better than the education of experts in the medical field.
Epistemic humility and a consequent reliance on domain experts is an essential part of being informed in our wonderfully complex world. This also means it is possible to be mislead by experts who are in the wrong, but I don't really see how this can be entirely avoided.