If the vaccines are a poison, then Trump would be complicit in a crime by agreeing to a contract involving that crime.

No contract that mandates illegal behavior is enforceable in court nor can it be used as an effective defense in court.

If the vaccine is dangerous, and Trump knows it, a contract is not going to be able to stop him from saying something if he wants to.

Trump would not be confused about that. He has more than a little experience dealing with legal contracts.

If the vaccines are a poison, then Trump would be complicit in a crime by agreeing to a contract involving that crime.

No contract that mandates illegal behavior is enforceable in court nor can it be used as an effective defense in court.

If the vaccine is dangerous, and Trump knows it, a contract is not going to be able to stop him from saying something if he wants to. And I doubt Trump would be confused about that.