Passive Immunity

  • Produced by the introduction of antibodies into individuals from an outside source
  • No direct contact with the pathogen or its antigens is necessary to induce immunity; immunity is acquired immediately
  • As the antibodies are not being produced by the individuals themselves, the antibodies are not replaced when they are broken down
  • No memory cells are formed and so there is no lasting immunity
  • Examples include antivenom or in the antibodies carried from the mother to the foetus


Active Immunity

  • Produced by stimulating the production of antibodies by the individuals own immune system
  • Direct contact with the pathogen or its antigen is required
  • Immunity takes time to develop
  • It is generally long lasting through the production of memory cells
  • Active immunity has two types:
  • Natural active immunity: Results from an individual becoming infected with a disease under normal circumstances. The body produces its own antibodies and may continue to so for many years
  • Artificial Active Immunity: Forms the basis of vaccinations, it involves inducing an immune response in an individaul without them suffering the symptoms by injecting dead/inactive pathogens into the patient’s body


Antigenic Variability

  • Antigens on the cell surface of a pathogen are used to activate the immune system. However, these antigens can change, through antigenic variability which occurs as a result of the change in the genes through mutations
  • The changes to the antigens means that when you are infected with the pathogen, the pathogen cannot be identified by the immune system and is therefore treated as a primary immune response (as it is considered new)
  • Antigenic variability is therefore harder to vaccinate against as they are always changing
  • Influenza virus and HIV are examples of pathogens which have antigenic variability, hence why flu vaccinations have to be had every year.