Vaccines

• Immunity


  The body's ability to resist infection or disease
• Vaccine


  A substance used to stimulate the production of antibodies and provide immunity against one or several diseases
• Immune system


  • Innate (natural) immunity
  • Adaptive (Acquired) immunity
• Innate (natural) immunity


  The body's first line of defence against infection, including physical, chemical and cellular barriers, but does not have memory
• Adaptive (Acquired) immunity


  The body's second line of defence, increases in strength and effectiveness with each encounter, and has memory of previous infections
• Passive immunity


  1. Natural maternal transfer of antibodies

  2. Artificial administration of preformed substance to provide immediate but short-term protection
• Active immunity


  1. Natural - following contact with a micro-organism / antigen

  2. Artificial administration of agent to stimulate immune response (immunisation)
• Antigen


  A live or inactivated substance (e.g. protein or polysaccharide) capable of producing an immune response
• Antibodies


  • Different types (IgM, IgG, IgA, IgD, IgE)
  • Each antibody is specific for its antigen - no cross protection
  • Produced by plasma cells in large amounts when B cells come into contact with their matching antigen
• Antibody functions


  • Circulate and attack micro-organisms
  • Block adhesion / cell entry of the antigen
  • Neutralise and prevent organism's replication
  • Signal macrophages and other WBCs to come
  • Kill organism via complement proteins - lysis
  • Neutralise toxin
• Immune response


  1. Primary immune response (mainly IgM antibody)

  2. Secondary immune response (faster and more powerful, predominantly IgG antibody)
• How vaccines work


  • Induce active immunity
  • Immunity and immunologic memory similar to natural infection but without risk of disease
• Aim of vaccine is to produce the same immune protection which usually follows natural infection but without causing disease, and generate long-lasting immunity and interrupt spread of infection
• Immunisation


  Receiving a vaccine and becoming immune to a disease, as a result of being vaccinated
• Vaccination


  Having a vaccine - actually getting the injection
• Live Attenuated Vaccines


  • Weakened viruses / bacteria
  • Stimulates immune system to react as it does to natural infection
  • Produces long lasting immune response after one or two doses
  • Can cause mild form of the disease
• Inactivated Vaccine and Toxoid

  • Inactivated by chemical process or heat
  • Cannot cause the disease they are designed to protect against
  • Doses: Two or more doses plus booster doses usually required
• Vaccine failure can occur due to simultaneous administration of immunoglobulin, immunosuppression, sickle cell disease and other causes of hyposplenism, malnutrition and chronic disease, nephrotic syndrome, and prematurity
• Herd immunity


  The indirect protection from infection of susceptible members of the population, and the protection of the population as a whole, which is brought about by the presence of immune individuals
• To achieve herd immunity, the percentage of individuals who need to be vaccinated depends on the disease and the vaccines used
• Herd immunity is the most effective way of protecting people who do not respond to vaccines or can't be given them for medical reasons