Don't make the vaccine mandatory -- yet.

"If we force people to opt in, that will not have as positive an effect on the other 324 million Americans that aren't in the Department of Defense," said Navy SEAL Commander Mike Hayes. "And ultimately what it's about is influence, positivity and not forcing the issue." [Source]

I agree with that. It's still a bit too early to force it.
Let the early adopters go first, and let the hesitant see the results.

"I’ve been talking to people who’ve got the vaccine ... I’m comfortable with that now," said Staff Sgt Keara Holbrook. "We just have to really get off of social media and think for ourselves and actually do the research," Holbrook added.