Vaccines usually don't cause problems, but when they do it is very hard to get those statistics collected. I do have a coworker who lost her hearing due to a bad vaccine. My daughter did have a minor side effect from the measle/chicken pox vaccine. The side typical side effects from each of those vaccines are similar, but since it was a combination vaccine, I'll never know which one/both my daughter had a reaction to. The pediatricians did not care and said it's hard to get the CDC to collect feedback like this. I would argue for singular vaccines and blood test for pre-disposed reactions. In my opinion it's hard to push good science to the medical community, so approaches like this seem to go nowhere.