Besides standard talking points, always bring up the "thalidomide children"

https://en.m.wikipedia.org/wiki/Thalidomide

In short - a few decades ago there was a quite tragic period of many birth defects caused by mothers taking the drug. It was anti-nausea drug.

Not properly tested medicine which led to unforeseen tragedy. Unforeseeable tragedy - it couldn't be predicted due to lack of proper testing. Just like the current vaccines.

Maybe it will help.