A heterologous vaccine (also known as a 'Jennerian' vaccine) is a type of live vaccine where one pathogen is introduced in order to provide protection against a different one. The vaccines are pathogens of other animals that either do not cause disease or cause mild disease in the organism being treated. A heterologous vaccine (also known as a 'Jennerian' vaccine) is a type of live vaccine where one pathogen is introduced in order to provide protection against a different one. The vaccines are pathogens of other animals that either do not cause disease or cause mild disease in the organism being treated.