What was the original definition?
Easily searchable but:
OLD:
‘A preparation of killed microorganisms, living attenuated organisms or living fully virulent organisms that is administered to produce or artificially increase immunity to a particular disease’
NEW:
‘a preparation that is administered (as by injection) to stimulate the body’s immune response against a specific infectious agent or disease: such as a: an antigenic preparation of a typically inactivated or attenuated pathogenic agent (such as a bacterium or virus) or one of its components or products (such as a protein or toxin)’