The problem isn't with the understanding of how vaccines work, the reason idiots don't want vaccines is they dont trust what you're telling them is the case.
In their mind, these soldiers you're training are better if they're naturally fit and learning how to fight through real world experience.
And this "training" you're giving your soldiers, is actually just Al-Qaeda's communist lgbtqia+/? agenda being pushed by Joe Biden and Alexandria Ocasio-Cortez (in their mind).
Here's the thing: you can't use logic to reason someone out of a position they didn't reason themselves into.