Vaccinations
Laura Armstrong
Teacher
Contents
Recall Questions
This topic requires prior knowledge of primary and secondary immune responses and antibody production. You can test your knowledge on these below.
What is an antigen?
A molecule, usually a protein, that triggers an immune response.
How do T-lymphocytes help in the immune response?
They activate B-cells, kill infected cells directly, and produce memory cells.
What is the role of plasma cells in immunity?
Plasma cells produce antibodies specific to a particular antigen.
Topic Explainer Video
Check out this @LauraDoesBiology video that explains vaccinations or read the full notes below. Once you've gone through the whole note, try out the practice questions!
How Vaccinations Lead to Immunity
- Vaccines contain antigens from a pathogen, which stimulate the immune system to produce a primary immune response, this is an example of artificial, active immuntiy.
- These antigens may be on a dead or weakened pathogen or may just be the isolated antigen.
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Live Attenuated Vaccines contain a weakened (attenuated) form of the pathogen that can replicate but does not cause disease. This could lead to infection in immunocompromised individuals.
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Inactivated (Killed) Vaccines contain pathogens that have been killed by heat or chemicals but still have intact antigens. This type of vaccine often requires booster vaccines.
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- Once injected with the antigen, an immune response is triggered.
- B-lymphocytes produce plasma cells that secrete antibodies.
- Memory cells are produced, providing long-term immunity.
- On secondary exposure, memory cells respond quickly and produce antibodies faster, preventing symptoms of disease.
How Vaccines Prevent the Spread of Disease
- When vaccinated individuals encounter the same pathogen, their immune system rapidly destroys it.
- This reduces the chance of transmission of the pathogen to others.
- Some pathogens require a large host population to survive, so reducing the number of susceptible individuals can eradicate diseases (e.g., smallpox).
Herd Immunity
- When a large proportion of the population is vaccinated, non-vaccinated individuals are also protected.
- The pathogen has fewer hosts, reducing its spread.
- This is especially important for individuals who cannot be vaccinated, such as those with compromised immune systems.
- Threshold for herd immunity varies between diseases (e.g., measles requires ~95% vaccination coverage).
Challenges of Antigenic Variation
- Some pathogens, like influenza and HIV, undergo frequent antigenic variation (changes in surface antigens), this is due to mutations in the genetic material of the pathogen.
- This means memory cells from previous infections or vaccinations do not recognise the antigens of new strains.
- Annual vaccines are required for diseases with high antigenic variation.
- Pathogens like HIV evade the immune system by rapidly mutating.
Key Terms
- Vaccine: A substance containing antigens that stimulates an immune response.
- Antigenic variation: Changes in surface antigens that prevent recognition by memory cells.
- Herd immunity: Protection of non-vaccinated individuals due to widespread vaccination.
- Live-attenuated vaccine: A vaccine using weakened forms of the pathogen.
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Exam Tip
Remember, mutations happen randomly, be careful not to imply that viruses, like HIV or influenza, mutate on purpose to evade the immune response!
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Influenza viruses frequently undergo antigenic variation, making it difficult to develop long-lasting vaccines. The H3N2 strain is an example of an influenza A virus that has caused multiple outbreaks due to changes in its surface proteins.
Describe how antigenic variation in influenza viruses can reduce the effectiveness of vaccines. (3 marks)
- Surface antigens of the virus change due to mutations
- Memory cells from previous infection or vaccination do not recognise new antigens
- Immune system must start a new primary response, slowing protection.
Practice Question
Try to answer the practice question from the TikTok on your own, then watch the video to see how well you did!