Or long term alien invasions! There's no proof that giving vaccines won't result in a pulse being sent out that attracts aliens from Mars.I don't disagree.
That is not the same as ensuring no long - term adverse effects. Only elapsed time can do that.
That's a different situation to long - term adverse effects.
Then again, neither are particularly plausible.
Some people have been using the drug thalidomide as a scare story. Which is misleading as conventional current testing would identify the thalidomide problems and because it's not a vaccine. I hear the Titanic sank, so it's not safe to fly.