immunity and vaccinations

• Active immunity


  the type of immunity you get when your immune system makes its own antibodies after being stimulated by an antigen.
• active natural immunity 


  when you become immune after catching a disease. e.g. if you have measles as a child, you shouldn't be able to catch it again in later life.
• active artificial immunity 


  when you become immune after you've been given a vaccination containing a harmless dose of antigen
• Passive immunity


  the type of immunity you get from being given antibodies made by a different organism - your immune system doesn't produce any antibodies of its own.
• natural passive immunity 


  when a baby becomes immune due to the antibodies it receives from its mother, through the placenta and in breast milk.
• passive artificial immunity 


  when you become immune after being injected with antibodies from someone else. E.g. if you contract tetanus you can be injected with antibodies against the tetanus toxin, collected from blood donations.
• Active Immunity

  • Requires exposure to antigen
  • It takes a while for protection to develop
  • Protection is long-term
  • Memory cells are produced
• Passive Immunity

  • No exposure to antigen
  • Protection is immediate
  • Protection is short-term
  • Memory cells aren't produced
• autoimmune disease


  an organism's immune system isn't able to recognise self-antigens- antigens present on the organism's own cells. When this happens, the immune system treats the self-antigens as foreign antigens and launches an immune response against the organism's own tissues.
• While your B lymphocytes are busy dividing to build up their numbers to deal with a pathogen (i.e. the primary response), you suffer from the disease. Vaccination can help avoid this.
• Vaccines contain substances that cause your body to produce memory cells against a particular pathogen, without the pathogen causing disease. This means you become immune without getting any symptoms.
• The substances in the vaccine may be antigens, which could be free or attached to a dead or attenuated (weakened) pathogen. The substances can also be other molecules, such as mRNA (see p.96) designed to code for antigens found on a pathogen. When the mRNA enters the body cells, it provides the instructions needed for cells to produce these antigens, which triggers memory cells to be made.
• Vaccines may be injected or taken orally. The disadvantages of taking a vaccine orally are that it could be broken down by enzymes in the gut or the molecules of the vaccine may be too large to be absorbed into the blood. Sometimes booster vaccines are given later on (e.g. after several years) to make sure that more memory cells are produced.
• Epidemics (mass outbreaks of disease) can be prevented if a large percentage of the population is vaccinated. That way, even people who haven't been vaccinated are unlikely to get the disease, because there's no one to catch it from. This is called herd immunity.
• Vaccination is not the same as immunisation. Vaccination is the administration of a substance designed to stimulate the immune system.

  Immunisation is the process by which you develop immunity. Vaccination causes immunisation.
• Vaccinating against a disease isn't always straightforward. For example, some sneaky pathogens can change their surface antigens. This means that when you're infected, the memory cells produced following a vaccination will not recognise the different antigens. So the immune system has to start from scratch and carry out a primary response against these new antigens. For this reason, a vaccine and vaccination programme may have to change regularly.