immunisation

• Immunity can be developed by vaccination using antigens from infectious pathogens, so creating memory cells.
• Antigens used in vaccinations can be:

  • pathogen toxins
  • dead pathogens
  • parts of pathogens
  • weakened pathogens.
• Adjuvants are a substance which makes the vaccine more effective, so enhancing the immune response.
• • Herd immunity occurs when a large percentage of the population is immunised.
  • Establishing herd immunity is very 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 factors upon which herd immunity depends are:

  • The type of disease
  • The effectiveness of the vaccine
  • 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.
  • Vaccines are rejected by a percentage of the population in the developed world.
• Some pathogens can change their antigens. This means that memory cells are not effective against them
• Clinical trials are needed to establish safety and effectiveness before being licensed for use.
• Factors in clinical trials:

  
• RANDOMISED TRIALS

  All participants in the clinical trial are split into different groups entirely at random. A computer programme may be used. Randomising the participants reduces possible bias in the trial.
• PLACEBO-CONTROLLED

  A placebo is a 'dummy' treatment with no medical or therapeutic value. One group of participants will be given the drug and another control group will be given the placebo to ensure valid comparison. It is important that participants are not aware of which group they are in.
• DOUBLE-BLIND TRIAL

  In a double-blind trial, neither the participants nor the researchers are aware which group has been given the drug and which group has been given the placebo. This also reduces bias when interpreting the results.
• Vaccines do not cause disease in vaccinated individuals because they contain weakened pathogens.