Here's my take on it.

One of the hallmarks of Trump's presidency is his doctrine of Principled Realism.

As I understand it, that means you may not approve of someone or something, but you will work with him or her to get things done.

So he may not believe in this vaccine, but he knows other people want it, demand it, even. You cannot change their minds without their blowing a gasket -- and they have the right to take a vaccine, even if you wouldn't do it yourself.

Individual choice.

Furthermore, if Trump is going to do something, he's going to be the best at it.

Hence he pushes to get the vaccine ready for those who want it; faster and cheaper than ever before.

Could be wrong, but that's my perspective.

And I love my president (Trump, that is), but I have absolutely no intention of EVER accepting that mark of the beast.