From everything I’ve seen, and from a lot of sources, the Pfizer vaccine is notably less effective at preventing breakthrough cases. That said, it’s still preventing cases, and just as effective at preventing serious breakthrough cases. The majority of people I know who’ve had breakthrough cases were vaccinated with Pfizer, but I know one or two that got it after moderna. I don’t know what difference between the two has made one less effective, but I’m glad I got moderna. We had a major COVID outbreak in my school district that lasted three or four weeks after school started. My teaching assistant had a breakthrough case after taking the Pfizer, and I spent several hours within a few feet of her the day she developed symptoms and did not get sick. 5 days later an unvaccinated teacher who I’d been around for several hours got sick, and I again didn’t get sick. The other unvaccinated teacher on our team got it from her and developed symptoms 5 days later. Again I was around her quite a bit and didn’t get sick. So as best I can tell, considering that I’ve never (knowingly) had COVID, I’m pretty confident in saying that the vaccine to this point has kept me from getting sick.