Vaccines
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Immunity can be developed by vaccination using antigens from infectious pathogens, so creating memory cells.
The antigens used in vaccines can be inactivated pathogen toxins, dead pathogens, parts of pathogens and weakened pathogens.
Adjuvant
antigens are usually mixed with an adjuvant when producing the vaccine. An adjuvant is a substance which makes the vaccine more effective, so enhancing the immune response.
Herd Immunity
Herd immunity occurs when a large percentage of a population is immunised. Establishing herd immunity is important in reducing the spread of diseases. Non-immune individuals are protected as there is a lower probability they will come into contact with infected individuals. The herd immunity threshold depends on the type of disease, the effectiveness of the vaccine and the density of the population.
How Herd Immunity protects the non vaccinated
Non-immune individuals are protected as there is a lower probability they will come into contact with infected individuals.
Mass Vaccination Progarammes
Mass vaccination programmes are designed to establish herd immunity to a disease.
Difficulties in programs
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.
Antigenic Variation
Some pathogens can change their antigens. This means that memory cells are not effective against them.
Role and impact of antigenic variation in influenza
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 year.