Why Is Vaccination Used?
- Infectious diseases trigger immune responses that take time.
- When a pathogen enters the body for the first time, the immune response is slow.
- Symptoms develop while the immune system learns how to respond.
- Vaccination reduces or prevents this delay
- It exposes the immune system to pathogen antigens in advance.
- Protection occurs before real infection happens.
- This means vaccination is about timing, not strength.
- The immune response happens earlier, not differently.
How Does Vaccination Work?
- Vaccination introduces antigens without causing disease
- A vaccine contains antigens, instead of a fully functioning pathogen.
- These antigens may be:
- Weakened (attenuated) forms of a pathogen.
- Inactivated (killed) pathogens.
- Specific pathogen fragments, usually surface proteins.
- Genetic instructions that allow cells to produce a harmless antigen.
- Antigens Are Recognized As Foreign
- Antigens are detected by white blood cells in the immune system.
- Specialized immune cells display antigens to lymphocytes, signalling a potential threat.
- Lymphocytes Produce Specific Antibodies
- B lymphocytes produce antibodies that bind to a specific antigen.
- Each antibody has a unique shape that matches only one antigen.
- This specificity ensures the response targets the correct pathogen.
- Memory Cells Are Formed
- Some activated lymphocytes differentiate into memory cells.
- Memory cells remain in the body long term.
- They enable a faster and stronger secondary immune response.
- Rapid Secondary Response Prevents Disease
- If the real pathogen enters the body later:
- Memory cells recognize the antigen immediately.
- Antibodies are produced rapidly in high concentration.
- The pathogen is eliminated before symptoms develop.
- If the real pathogen enters the body later:
Antigen
A molecule, usually a protein, that is recognised as foreign by the immune system and triggers an immune response.
Antibody
A protein produced by B lymphocytes that binds to a specific antigen to help neutralize it.
- Think of vaccination as saving a contact in your phone.
- You do not need to search for your friend's number each time, and can also reply instantly when you see their notification.
- Thinking vaccines kill pathogens directly.
- Vaccines train the immune system. They are not medicines.
Why Do Some Diseases Disappear And Others Persist?
- Eradication occurs when transmission stops completely.
- A disease is eradicated when it no longer exists in the human population.
- This requires:
- Effective vaccines
- Sustained high vaccination coverage worldwide
- No non-human reservoirs
- Herd immunity limits disease spread
- When most individuals are immune, pathogens struggle to spread.
- Transmission chains are broken.
- Unvaccinated individuals receive indirect protection.
- Some diseases are difficult to eradicate, which occurs when they:
- Have animal reservoirs
- Mutate rapidly
- Experience reduced vaccination uptake, allowing diseases to re-emerge.
Herd immunity
Protection of a population when a sufficiently high proportion is immune, reducing disease transmission.
Reservoir
Any population where a pathogen can live, survive, and reproduce over time.
- Smallpox
- The last natural case occurred in 1977.
- Declared eradicated in 1980.
- A virus spreads like a rumor.
- If most people refuse to pass it on, it dies out.
What Are The Main Types Of Vaccines?
| Vaccine type | What's included | Immune response | Limitations | Example |
|---|---|---|---|---|
| Live attenuated | Weakened pathogen | Strong and long-lasting | Unsafe for immunocompromised | MMR |
| Inactivated | Killed pathogen | Moderate | Boosters required | Polio |
| Subunit | Specific proteins | Safe and targeted | Multiple doses | HPV |
| mRNA | Genetic instructions | Strong and specific | Storage requirements | COVID-19 |
What Are The Benefits And Risks Of Vaccination?
- Benefits
- Prevents serious infectious diseases.
- Reduces disease transmission.
- Protects vulnerable individuals.
- Enables disease eradication.
- Risks
- Mild side effects such as soreness or fever.
- Very rare allergic reactions.
At a population level, benefits outweigh risks.
Why Is Vaccination Essential For Public Health?
- Prevention of outbreaks
- Maintains herd immunity.
- Prevents rapid spread in communities.
- Cost-effective healthcare
- Reduces hospital admissions.
- Lowers long-term healthcare costs.
- Protection of vulnerable groups
- Infants.
- Elderly individuals.
- Immunocompromised patients.
- Assuming vaccination only protects the individual.
- Vaccination is a population-level strategy.
- How does vaccination create immunity without causing disease?
- Why are memory cells essential for long-term protection?
- Explain how herd immunity protects unvaccinated individuals.
- State two reasons why some diseases are difficult to eradicate.