Lecture Notes: Understanding Vaccines and Immune System

Introduction to the Immune System and Vaccines

• Vaccines prepare the immune system to fight pathogens (disease-causing organisms).
• Immune System Response:
  • Innate Immune System:
    • First line of defense.
    • Immediate, non-specific response (destroys all foreign invaders indiscriminately).
    • Signs include fever.
  • Adaptive Immune System:
    • Activates if innate immunity fails.
    • Produces antibodies specific to antigens on pathogens.
    • Leaves a "memory" for faster future responses (immunity).

Immunity

• Pathogen-specific antibodies are produced quickly upon re-exposure, often preventing symptoms of illness (e.g., chickenpox immunity).

How Vaccines Work

• Vaccines introduce an altered form/part of a pathogen to stimulate antibody production without causing illness.
• Prepares immune system for fast response to actual pathogen exposure.
• Herd Immunity:
  • Occurs when a significant portion of a community is vaccinated.
  • Protects unvaccinated individuals (e.g., very young, old, immunocompromised).
  • Relies on sufficient number of vaccinated individuals to act as "firebreaks" against disease spread.

Types of Vaccines

1. Live, Attenuated Vaccines:

   • Use weakened live pathogens.
   • Highly effective, potential for life-long immunity.
   • Not suitable for immunocompromised individuals.

2. Inactivated Vaccines:

   • Pathogens completely inactivated.
   • Safer than live vaccines, but less effective.
   • May require multiple doses.

3. Subunit Vaccines:

   • Use only parts of a pathogen (e.g., peptide).
   • Very safe (cannot cause disease).
   • Require identification of effective pathogen part, which can be challenging.

4. Toxoid Vaccines:

   • Target bacterial toxins.
   • Toxins inactivated and used to induce antibody production.

5. Conjugate Vaccines:

   • Target bacteria with protective coats.
   • Combine weak antigens with strong antigens to enhance immune response.