"What’s required for a vaccine to be 100% effective at preventing infection
In order to entirely prevent infection, vaccines would need to induce what’s called “sterilizing immunity,” a type of immunity that prevents a pathogen—in this case the coronavirus—from infecting any cells. If the virus cannot infect cells, then the host (in this case, a person) cannot transmit it to others.
In a best-case scenario, all vaccines would provide sterilizing immunity, meaning they would protect against disease and prevent transmission. But in practice, most vaccines don’t do this. The influenza, rotavirus, and pertussis vaccines, among others, can prevent serious illness from developing, but they don’t reach the level of sterilizing immunity."