All they did was add this: "b : a preparation of genetic material (such as a strand of synthesized messenger RNA) that is used by the cells of the body to prod

All they did was add this: "b : a preparation of genetic material (such as a strand of synthesized messenger RNA) that is used by the cells of the body to produce an antigenic substance (such as a fragment of virus spike protein)" to what existed before: "a : an antigenic preparation of a typically inactivated or attenuated (see attenuated sense 2) pathogenic agent (such as a bacterium or virus) or one of its components or products (such as a protein or toxin)"