Prove Him Wrong
It’s clear that this person has no idea what a vaccine does. No one knows where he got his information, but it’s inaccurate nonetheless. Fortunately, he was put in his place by the person who left a comment. That we have to rely on people who we don’t know to bring some sense to the world is a pity.
People who post things like this on multiple social media accounts are likely to do so frequently. Take a breather and think about what it would be like to have so many wrong answers all the time. Even worse, this person is wrong and proud of it, all this requires a lot of confidence and ignorance, surely.