No, we can't start throwing out burden of proof when it suits us.

I've argued elsewhere in this thread that the solution is to obligate parents to provide vaccinations, just like they're obligated to provide food, water, clothing, shelter, etc. This is the basic legal duty of care that all parents have towards their children, and it should extend to vaccines. This is both a logical application of existing law - rather than requiring new law - and incredibly simple to prove in court. If parents are obligated to vaccinate their kids, all a cop or social worker has to do is ask for the proof of vaccination. There's no balance of proof to consider, and no knotty problems of untangling exactly how someone else's kid got sick.

Honestly, I'd settle for disclosure, especially now that they're removing school requirements in some states. It would be worth it to me to know which kids/ parents to keep my kids away from.