"Purchaser acknowledges the long-term effects and efficacy of the Vaccine are not currently known and that there may be adverse effects of the Vaccine that are not currently known."
“There are known knowns — there are things we know we know. We also know there are known unknowns — that is to say, we know there are some things we do not know. But there are also unknown unknowns, the ones we don’t know we don’t know.”
Donald Rumsfeld quote.
The above in my mind is a really good statement to remember. Especially when making a risk assessment.