Two vaccines have brought us to the brink of a polio-free world: the oral polio vaccine and the inactivated polio vaccine. Learn how these vaccines work and the different, complementary roles they have to play in delivering a polio-free world. This is one of a series of six videos on what is being done to secure a polio-free world: from the vaccines that are being used to stop polio; to how the oral polio vaccine is being phased out from April 2016 to remove any risk of vaccine-derived polioviruses, starting with the switch from trivalent to bivalent oral polio vaccine in April 2016; and how securely containing polioviruses within laboratories and vaccine manufacturing sites will keep every last child protected, long into the future.