Ch 17

Variolation (Inoculations)
  - Early method used to protect against smallpox.
  - Practiced in China during the Sung dynasty (960–1280).
  - Involved intentional exposure to materials from smallpox lesions.
  - Techniques included:
    - Grinding dried smallpox scabs into powder and blowing it into the nose.
    - Placing smallpox material directly into small cuts or scratches on the skin.
  - These methods exposed people to the virus to induce immunity.
  - Safety Concerns: Variolation was not safe by today’s standards; individuals could develop severe disease and spread it to others.
  - Knowledge of variolation spread to:
    - India
    - Middle East
    - Europe

Adoption of Variolation
- In Europe, variolation was used, but it remained a risky procedure.
Edward Jenner (1800s)
- Observed that milkmaids who contracted cowpox rarely developed smallpox.
- Identified that cowpox and smallpox are closely related viruses.
Hypothesis:
- Exposure to cowpox protects against smallpox.
Experiment Conducted:
  - Took material from cowpox blisters and inoculated a young boy.
  - The boy developed mild symptoms and recovered.
  - Later, Jenner exposed the boy to smallpox material, and the boy did not develop smallpox.
Terminology:
- Jenner coined the term "vaccination" from the Latin word "vacca," meaning cow.
Impact: Smallpox has now been completely eradicated!

Immunization: The process of inducing immunity to a disease.
- Has had the greatest impact on human health compared to any other medical procedure.
- Represents how knowledge can battle disease.
Vaccine Definition:
- A vaccine is a preparation of an antigen or its derivative used to induce immunity, protect an individual, and prevent transmission in the population.

Concept:
- Herd immunity develops when a critical proportion of the population is immune to a disease.
- The infectious agent is unable to spread due to insufficient susceptible hosts.
Outcome:
- Responsible for the dramatic decline in infectious diseases.
- Notable issue: Diseases can reappear and spread as a result of failure to vaccinate children.

Definition:
- Contain a weakened form of the living pathogen.
Characteristics:
  - The agent can replicate.
  - Induces a stronger immune response but may cause disease.
  - Grown under conditions that foster mutations or genetically manipulated to replace genes, both of which reduce pathogenicity.
Examples:
- Measles, mumps, rubella, chickenpox, yellow fever, rotavirus.
Advantages:
- A single dose usually induces long-lasting immunity due to microbial multiplication in the body.
Disadvantages:
  - Can sometimes cause disease in immunosuppressed individuals.
  - Can occasionally revert or mutate to become pathogenic.
  - Generally not recommended for pregnant women.
  - Usually require refrigeration.

Definition:
- The agent is killed or inactivated and cannot replicate.
Characteristics:
- Induces a weaker immune response but cannot cause infections.
Advantages:
- Cannot cause infections or revert to pathogenic forms.
- Suitable for immunocompromised individuals and pregnant women.
Disadvantages:
- Requires several doses or booster shots due to a less robust immune response.
Examples:
- Polio, rabies, hepatitis A.
Adjuvants: Substances included in inactivated vaccines to enhance the immune response:
- Thought to provide danger signals to dendritic cells.
- Some adjuvants hold the antigen and release it slowly over time, while others trigger an inflammatory response.

Inactivated Whole Agent Vaccines:
   - Contains the whole virus or bacterium that is killed or inactivated.
   - Treated with heat, irradiation, or chemicals without significantly altering surface characteristics.
   - Examples: Influenza, rabies, hepatitis A.
Toxoid Vaccines:
- Contain inactivated bacterial toxins rather than the whole bacteria.
- Examples: Diphtheria, tetanus.
Subunit Vaccines:
   - Consist of key antigens from pathogens rather than the whole pathogen.
   - Antigens could include proteins, polysaccharides, glycoproteins.
   - Recombinant Subunit Vaccines:
     - Use genetic engineering to produce specific subunits of a pathogen, e.g., hepatitis B virus proteins produced by yeast cells.
Polysaccharide Vaccines:
   - Contain polysaccharides from bacteria.
   - Not effective in young children due to polysaccharides being T-independent antigens, which elicit a poor response.
   - Example: Pneumococcal vaccine for adults.
Conjugate Vaccines:
- Link polysaccharides to proteins to convert them into T-dependent antigens.
- Example: Haemophilus influenzae type b (Hib) conjugate vaccine has greatly reduced Hib meningitis in children.
Nucleic Acid-Based Vaccines:
   - A promising area of research involving segments of naked DNA or RNA from infectious agents.
   - Some cells express genes for a short period post-injection, inducing an immune response.
   - Example: COVID-19 mRNA vaccine.

The benefits of vaccination significantly outweigh the very slight risks.
Example**:
- A child with measles has a 1 in 2,000 chance of serious brain inflammation compared to a 1 in 1,000,000 chance from the vaccine.
Historically, there were numerous deaths and disabilities prior to the advent of vaccinations.
Even today, many individuals still become ill or die from preventable diseases.

Some parents refuse to vaccinate their children due to fears of harm.
Misinformation:
- There is no evidence linking vaccines to autism.
- A discredited study falsely associated the MMR vaccine with autism, and although it was retracted, misinformation persists.
Role of Social Media:
- Accelerates the spread of misinformation, personal anecdotes, and conspiracy theories.
Outcome:
- Vaccines have become victims of their own success, as many people no longer recognize the seriousness of these diseases.

Adjuvants: Substances contained in vaccines to enhance the immune response include:
  - Adjuncts
  - Primary substances
  - Adjuvants
  - Secondary substances
Characteristics of Inactivated Vaccines:
  - All of the following are true regarding inactivated vaccines EXCEPT:
    - Elicit weaker immune response
    - Pathogen does not replicate
    - May cause disease in immunocompromised
    - Booster shot required