Vaccines
Biology: IB Diploma Higher Level, topic 11.2.5
Vaccination
Vaccines help the immune system recognise and destroy pathogens.
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
- 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
- The primary immune response leads to the production of memory cells.
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 can be given over time to make sure the memory cells are still in the body.
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
- 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
- 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
- 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:
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).
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).
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?