Enhanced pulmonary pathology in cotton rats upon challenge after immunization with inactivated parainfluenza virus 3 vaccines

Vaccine-induced potentiation was studied in cotton rats immunized with form alin-inactivated human parainfluenza type 3, ultraviolet light-inactivated virus, or infection with live virus. Immunized animals and unimmunized cont rols were later challenged by intranasal inoculation of live virus and eval uated for pulmonary pathology 4 days later. Animals immunized with either o f the inactivated vaccines developed marked peribronchiolitis, perivasculit is, and an alveolar cellular infiltration much more severe than seen in ani mals infected previously, or in unmanipulated but challenged animals, Disea se enhancement after immunization with killed virus is thus a characteristi c of a member of each of three genera of the family, Paramyxoviridae, and i s not restricted to immunization with formalin-inactivated virus.