Immunity is the ABSOLUTE Resistance to a pathogen considering that person has an INTACT IMMUNITY while susceptibility is the DEGREE of resistance. Degree of resistance means how well would the individual combat the pathogens and repel infection or invasion of these disease causing organisms. A susceptible person is someone who has a very low degree of resistance to combat pathogens. An Immune person is someone that can easily repel specific pathogens. However, Remember that even if a person is IMMUNE [ Vaccination ] Immunity can always be impaired in cases of chemotherapy, HIV, Burns, etc.