If La’an can still see the ghost, does that mean she is still infected? Or is the ghost the only entity that isn’t a hallucination?

I’d say, “Maybe?” That just seems like a horror trope, right? To dial the unease back up a little after the traditional catharsis? It’s honestly part of my issue with doing a different theme in most of the episodes. ST writers have never been as obsessed with consistent lore as the fans, but things like this go to the heart of what your audience wants from your show.