We’ll know BEFORE the election, no doubt about it. Trump always gets things done before deadline and under budget.
Any vaccine that Trump supports will be demonized as causing people to mutate into giant snails and be banned everywhere. They've set the pattern of successfully demonizing and banning medicine, they will just do it again. Once Trump is gone (by hook or by crook) they'll 'discover' that it's safe and effective. But not before.