Vaccination

• Vaccination

  1.Active immunity can be developed by vaccination with antigens from infectious pathogens, so creating memory cells.

  2.The Antigens used in vaccines can be dead and weakened pathogens

  3. Antigens are usually mixed with an adjuvant when producing the vaccine

  4. An adjuvant is a substance which makes the vaccine more effective, so enhancing the immune response.
• (b)Herd Immunity

  5. Herd immunity occurs when a large percentage of a population is immunised.

  6. Establishing herd immunity is important in reducing the spread of diseases.

  7. Non-immune individuals are protected as there is a lower probability they will come into contact with infected individuals.

  8. The herd immunity threshold depends on ; the type of disease, effectiveness of the vaccine and population density
• Antigenic Variation

  11. Some pathogens can change their antigens.

  12. This means that memory cells are not effective against them.

  13. The new strains of pathogens are described as demonstrating antigenic variation if they have antigens on their surface that are different to the original strain.

  14. Antigenic variation occurs in the influenza virus explaining why it remains a major public health problem and why individuals who are at risk require to be vaccinated every ye