Every exposure to COVID results in one of two possible outcomes: infection, or no infection. The COVID vaccines without a doubt increase the frequency of the second outcome and decrease the first, although their efficacy by this metric has been waning for over a year (they still seem superb at preventing serious illness and death). "Infections" doesn't mean "people who have ever been infected," which at this point is approaching 100% of the human population, it means "infections." The COVID vaccines prevent infections.