2.6.1 Vaccines

How Vaccines Work:

1. Composition:

• Vaccines may contain:
• Inactivated pathogens (killed microorganisms).
• Attenuated pathogens (weakened microorganisms).
• Toxoids, which are harmless forms of toxins produced by pathogens.
• Antigen fragments from the pathogen's surface.

2. Immune Response:

• The immune system recognises the antigens in the vaccine as foreign.
• B lymphocytes produce specific antibodies and form memory B cells.
• These memory cells persist in the body, enabling a rapid response if the pathogen is encountered again.

Factors Affecting the Success of Vaccination Programmes:

3. Cost:

• The vaccine must be affordable, especially in low-income countries.

4. Side Effects:

• Vaccines with severe side effects may discourage uptake.

5. Ease of Production, Storage, and Distribution:

• Vaccines need to be produced on a large scale and remain stable during transport and storage.

6. Coverage:

• A high percentage of the population must be vaccinated to achieve herd immunity.

Herd Immunity:

7. Definition:

• Herd immunity occurs when a large proportion of the population is vaccinated, reducing the spread of a pathogen.

8. How It Works:

• Vaccinated individuals protect those who are unvaccinated by preventing the pathogen from spreading.
• This is particularly important for those who cannot be vaccinated, such as individuals with weakened immune systems.

Limitations of Vaccines:

9. Antigenic Variation:

• Some pathogens, such as the influenza virus, frequently mutate, changing the structure of their antigens.
• This reduces the effectiveness of existing vaccines, requiring new formulations for continued protection.

10. Insufficient Uptake:

• If a significant portion of the population refuses vaccination, herd immunity may not be achieved, leading to outbreaks.

11. Pathogen Accessibility:

• Some pathogens hide inside host cells or mutate to avoid detection by the immune system.

Example: Influenza Virus:

• The influenza virus undergoes frequent mutations, leading to changes in its surface antigens.
• Vaccines need to be updated regularly to match the new strains, which limits the duration of immunity.