3.7

• Adjuvant


  A substance which makes the vaccine more effective, so enhancing the immune response
• Antibody


  1. shaped proteins that have receptor binding cites specific to a particular antigen on a pathogen. Antibodies become bound to antigens, inactivating the pathogen. The resulting antigen-antibody complex can then be destroyed by phagocytosis
• Antigen


  Molecules, often proteins located on the surface of cells that trigger a specific immune response
• Disease


  Illness affecting plants and animals
• Herd immunity


  The protection given to a population against an outbreak of a specific disease when a very high percentage of the population have been vaccinated against it
• Herd immunity threshold


  The number of immune individuals above which a disease may no longer circulate
• Immunity


  When a person's body is not prone to a disease because they have a resistance to it
• Lymphocytes


  White blood cells which produce antibodies to attack pathogens
• Measles


  An infectious disease of the respiratory system caused by a virus
• Memory cells


  Long lived lymphocyte that has previously encountered a given antigen and that on re-exposure to the same antigen rapidly initiates the immune response or proliferates and produces large amounts of specific antibody
• Mumps


  A viral disease that usually affects the salivary glands but can affect fertility in teenage boys and men
• Pathogen


  Microorganism that causes disease
• Phagocytosis


  Involves the engulfing of pathogens and their destruction by digestive enzymes contained in Lysosomes
• Primary infection


  The first time an organism becomes infected by a particular pathogen
• Rubella


  Also known as German measles, this is a viral disease with mild symptoms that can be very serious if contracted by a pregnant woman
• Vaccine


  Substances containing disabled antigens of a particular disease, usually administered via injection. Vaccines stimulate the body to produce antibodies to provide immunity against that disease
• White blood cell


  A type of cell found in blood that defends in infection
• Immunity to a pathogen can be developed by vaccination using antigens from infectious pathogens, so creating memory cells
• Antigens used in vaccines

  • Inactivated pathogen toxins
  • Dead pathogens
  • Parts of pathogens
  • Weakened pathogens
• Antigens are usually mixed with an adjuvant when producing the vaccine
• Vaccination


  1. Causes the immune system (specifically the white blood cells) to produce complementary antibodies, which target and attach to the antigen

  2. The white blood cell then digests the pathogen by phagocytosis
• Vaccination acts as the primary infection that results in more rapid immune response to a secondary infection
• Rapid immune response to the secondary exposure to the same pathogen is due to memory cells responding quickly in order to produce lots of relevant antibodies, which prevents infection. This is called being immune to a disease or having immunity
• Antigenic variation


  Some pathogens can change their antigens, meaning that memory cells are not effective against them
• Antigenic variation occurs in the influenza (flu) virus explaining why it remains a major public health problem
• New vaccines to target altered antigens in new "strains" of flu are designed each year and individuals who are at risk require to be vaccinated every year
• Herd immunity


  Occurs when a large percentage of a population is immunised. Establishing herd immunity is important in reducing the spread of diseases. Herd immunity ensures non-immune individuals are protected as there is a lower probability they will come into contact with infected individuals
• Herd immunity threshold


  Depends on the type of disease, the effectiveness of the vaccine and the density of the population
• Mass vaccination programmes are designed to establish herd immunity to a disease
• Difficulties can arise when widespread vaccination is not possible due to poverty in the developing world, or when vaccines are rejected by a percentage of the population in the developed world
• Herd immunity only works for diseases that are spread directly between people
• Herd immunisation can be less effective in centres of high population density where lots of people regularly come into daily contact