1. What are Vaccines?

Vaccines are biological preparations that provide acquired immunity to specific infectious diseases. They typically contain agents resembling a disease-causing microorganism, often in weakened or inactivated forms, or as fragments (e.g., proteins, mRNA).

Types of Vaccines

  • Live attenuated vaccines: Use weakened forms of the pathogen (e.g., measles, mumps, rubella).
  • Inactivated vaccines: Contain killed pathogens (e.g., polio, hepatitis A).
  • Subunit, recombinant, polysaccharide, and conjugate vaccines: Include only parts of the pathogen (e.g., HPV, pneumococcal).
  • mRNA vaccines: Deliver genetic instructions for cells to produce pathogen proteins (e.g., COVID-19 vaccines).
  • Vector vaccines: Use harmless viruses to deliver genetic material (e.g., Ebola, some COVID-19 vaccines).

2. How Vaccines Work

Vaccines stimulate the immune system to recognize and combat pathogens. They โ€œtrainโ€ immune cells to respond rapidly and effectively upon future exposure.

Immunity Flowchart

Immunity Flowchart

Flowchart Steps:

  1. Vaccine introduced into the body.
  2. Antigen-presenting cells (APCs) process vaccine components.
  3. APCs activate helper T cells.
  4. Helper T cells stimulate B cells and cytotoxic T cells.
  5. B cells produce specific antibodies.
  6. Cytotoxic T cells destroy infected cells.
  7. Memory cells are generated for long-term immunity.

3. Immunity Explained

Immunity is the bodyโ€™s ability to resist infection. It can be:

  • Innate: Non-specific, immediate defense (skin, phagocytes).
  • Adaptive: Specific, slower response (antibodies, memory cells).

Adaptive Immunity Steps

  • Recognition: Immune cells detect antigens.
  • Response: Production of antibodies and activation of killer cells.
  • Memory: Formation of memory cells for future protection.

4. Surprising Facts

  1. Bacteria in Extreme Environments: Some bacteria thrive in deep-sea hydrothermal vents, acidic hot springs, and even radioactive waste (e.g., Deinococcus radiodurans).
  2. Vaccines Can Target Cancer: Therapeutic vaccines are being developed to train the immune system to attack cancer cells (e.g., HPV vaccine reduces cervical cancer risk).
  3. Immunity Can Be Enhanced by Microbiome: Gut bacteria influence vaccine effectiveness and immune responses.

5. Global Impact of Vaccines

  • Eradication of Diseases: Smallpox eradicated (1980), polio nearly eliminated.
  • Reduction in Child Mortality: Immunization prevents 2โ€“3 million deaths annually (WHO).
  • Economic Benefits: Vaccines reduce healthcare costs and improve productivity.
  • Equity Challenges: Low-income countries face barriers in vaccine access and distribution.

Global Vaccination Coverage (2022)

  • DTP3 (Diphtheria, Tetanus, Pertussis): 81%
  • Measles: 83%
  • COVID-19: Over 70% of global population received at least one dose

6. Latest Discoveries (2020+)

  • mRNA Vaccine Technology: Rapid development and deployment for COVID-19, now being tested for influenza, Zika, and RSV.
  • Universal Flu Vaccines: Research aims to target conserved regions of influenza viruses for broader protection.
  • Personalized Vaccines: Cancer vaccines tailored to individual tumor mutations (neoantigen vaccines).
  • Microbiome-Vaccine Interaction: 2022 study in Nature Reviews Immunology highlights gut microbiotaโ€™s role in modulating vaccine responses and efficacy.

Citation:

  • Zimmermann, P., Curtis, N. (2022). The influence of the intestinal microbiome on vaccine responses. Nature Reviews Immunology, 22, 33โ€“46. Link

7. Unique Insights

  • Vaccine Hesitancy: Social media and misinformation challenge global immunization efforts.
  • Nanoparticle Vaccines: Use of nanotechnology to enhance delivery and stability of vaccine antigens.
  • Reverse Vaccinology: Computational methods to identify new vaccine targets from pathogen genomes.

8. Diagrams

Immune Response to Vaccines

Immune Response Diagram

9. Key Terms

  • Antigen: Substance that induces immune response.
  • Antibody: Protein produced by B cells to neutralize pathogens.
  • Memory Cell: Long-lived immune cell for rapid future response.
  • Adjuvant: Substance added to vaccines to boost immune response.
  • Herd Immunity: Protection of unvaccinated individuals due to high population immunity.

10. Summary Table

Vaccine Type Example Pros Cons
Live attenuated MMR Strong, long-lasting Not for immunocompromised
Inactivated Polio Safe, stable Weaker, may need boosters
Subunit HPV Targeted, safe May need adjuvants
mRNA COVID-19 Rapid development Storage challenges
Vector Ebola Strong cellular immunity Pre-existing immunity issues

11. Revision Questions

  1. How do mRNA vaccines differ from traditional vaccines?
  2. What role does the microbiome play in vaccine effectiveness?
  3. Name two diseases eradicated or nearly eradicated by vaccines.
  4. What are the advantages of nanoparticle vaccines?

12. References

  • Zimmermann, P., Curtis, N. (2022). The influence of the intestinal microbiome on vaccine responses. Nature Reviews Immunology, 22, 33โ€“46.
  • World Health Organization (WHO). Immunization coverage. Link