2.4.7

Vaccines

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Vaccination

Vaccines help the immune system recognise and destroy pathogens.

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Insertion of antigens

  • Vaccines insert the antigens for a specific disease into the individual.
  • The antigens can be inserted by:
    • Injection.
    • Oral insertion (oral vaccinations may be broken down in the stomach).
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Primary immune response

  • The presence of antigens in the body induces the primary immune response.
  • The antigens are inserted as a dead or weakened pathogen so the vaccine does not give rise to a full-scale infection with symptoms.
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Memory cells

  • The primary immune response leads to the production of memory cells.
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Immunity

  • Memory cells provide immunity.
  • If the individual is infected by a living pathogen, the memory cells will be ready to induce a fast, strong secondary response.
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Booster vaccinations

  • Booster vaccinations can be given over time to make sure the memory cells are still in the body.
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Continuous trial

  • Some vaccinations are continuously being changed because the antigens are evolving at a very rapid rate.
  • Pathogens evolve to avoid detection by the immune system. This causes a problem because it makes the vaccines useless.
  • Pathogens with a high mutation rate (e.g. influenza and HIV) are the most difficult to vaccinate against.

Herd Immunity

Herd immunity is the concept that if enough people in a population have immunity against a disease, the entire population are less likely to be infected.

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Spread of a pathogen

  • Herd immunity works if a large proportion of the population is vaccinated against a disease.
  • If most of the population are immune, the chance of someone without immunity coming into contact with the disease is reduced.
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Population requirements

  • Herd immunity is the basis of widescale vaccination programs.
  • If the disease is highly contagious (e.g. measles), over 90% of the population must be vaccinated.
  • If the disease is less contagious (e.g. polio), over 80% of the population must be vaccinated.
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Benefit

  • Herd immunity offers protection for the most vulnerable people in a population (e.g. new born babies and the elderly).

Active and Passive Immunity

Immunity can be provided in an active or a passive way. Active and passive immunity can also be artificial or natural. The different types of immunity are:

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Active immunity

  • Active immunity is where the immune system has created its own antibodies.
  • Active immunity can be:
    • Natural (antibodies have been created in response to catching a disease).
    • Artificial (antibodies have been created in response to vaccination of antigens).
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Passive immunity

  • Passive immunity is where an individual receives antibodies from an external source. The antibodies are not made by the individual.
  • Passive immunity can be:
    • Natural (antibodies are transferred to a baby from its mother in breast milk).
    • Artificial (antibodies are transferred to an individual by injection).

Jump to other topics

1Biological Molecules

2Cells

3Substance Exchange

4Genetic Information & Variation

5Energy Transfers (A2 only)

6Responding to Change (A2 only)

7Genetics & Ecosystems (A2 only)

8The Control of Gene Expression (A2 only)

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