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Vaccines

Biology: Cambridge International A Level, topic 11.2.4

Vaccination

Vaccines help the immune system recognise and destroy pathogens.

Insertion of antigens

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).
Primary immune response

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.
Memory cells

Memory cells

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

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.
Booster vaccinations

Booster vaccinations

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

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.

Spread of a pathogen

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.
Population requirements

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.
Benefit

Benefit

  • Herd immunity offers protection for the most vulnerable people in a population (e.g. new born babies and the elderly).
  • Herd immunity had a major impact on the eradication of smallpox. Herd immunity helped smallpox become eradicated.
Difficulties with vaccines

Difficulties with vaccines

  • Some diseases are harder to vaccinate & eradicate than others.
  • Vaccines for TB are not 100% effective. It's also difficult to deliver the vaccine to poor communities who need it most.
  • Measles has not been eradicated due to poor vaccine uptake. This occurred following a fabricated link between the vaccine and autism.
  • The malaria vaccine requires four shots and is not 100% effective. Not all patients return for all four shots.
  • Cholera is easily treatable with fluid replacement and antibiotics. The vaccine itself produces some sickness, so is avoided.

Test yourself on Vaccines

  • Which of the following statements about vaccines are true?

  • What cells provide long-lasting immunity?

  • What percentage of the population must be vaccinated to provide herd immunity for highly contagious diseases?

  • Which of the following statements about herd immunity are true?

  • Which members of the population does herd immunity protect?

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