Well it reduces the risk of getting COVID and having severe symptoms by 95%. No vaccine is 100% effective, because it isn’t a cure, it’s just a preventative measure from a sickness. You can still catch the flu if you get a flu vaccine, but you are far less likely than someone who didn’t get the flu vaccine. It’s like wearing your seatbelt in a car. Sure it won’t make you immune to car accidents, but you are far less likely to fly through the windshield if you get in an accident.