I passed it at 7 and it wasn't easy. I have personal experience of it being nasty, anti-vaxxers mostly don't. They don't even know what they're talking about because that's the whole point of their position, ignore every actual piece of knowledge about this and construct an very entertaining conspiracy that has no consequences until herd immunity crumbles. I don't even know why we're having this problem, we were on our way to eradicate measles, as we did with smallpox.