This is anon's $0.02 on this issue:
Many people are overlooking a few critical things here.
Trump is a very humble guy - it takes a lot of humility to put yourself in the ring like he has for all these years, and stay relatively unfazed and lighthearted.
If the goal was and is to have the bulk of the left (who are all brainwashed) and the boomer / RINO right (who are also brainwashed) join with the awake in condemning the vaccines to that there can be critical mass that stops continued bioweapon attacks on us, then there needed to be an easy "out" for them. That easy out is for them to blame it all on Trump.
I believe he is not going hard against the vax because it would cause the retards on the left and RINOs to further dig in their heels and prolong this.