By promoting it he is just the same as everyone else - so cannot be singled out as an antivaxer for one, secondly he can legit claim to also be a victim of the bad information being pedaled. Afterall he is "not a doctor", he only takes advice on that front. So the doctors pedaling it will be guilty of deceiving a President (when he reassumes that office openly). Then he can go on the attack because they "fooled" him.

Collatoral damage is unavoidable anyway, as people are taking it mainly on the advice of bad scientists rather than the advice of Trump, a non doctor.