Types of Vaccines

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Vaccine Classification - Shield Basics

  • Live-attenuated: Weakened pathogen; robust, often lifelong immunity.
  • Inactivated: Killed whole pathogen; multiple doses often needed.
  • Subunit: Uses specific antigenic parts; lower adverse reaction risk.
  • Toxoid: Chemically inactivated toxins; elicits anti-toxin antibodies.

⭐ Adjuvants (e.g., Alum) are often required for inactivated, subunit, and toxoid vaccines to enhance immunogenicity.

Live Attenuated Vaccines - Tamed Titans

  • Contain weakened (attenuated) live pathogens; mimic natural infection.
  • Immunity: Strong, long-lasting (humoral & cell-mediated); often 1-2 doses.
  • Pros: Potent immunity, herd immunity possible (e.g., OPV).
  • Cons:
    • Rare reversion to virulence.
    • Cold chain essential.
    • Avoid in pregnancy & immunocompromised individuals.
  • 📌 "BOY! THIS LIVE RUBE YELLOW": BCG, OPV, Yellow Fever, Typhoid (oral), Influenza (intranasal), Varicella, Epidemic Typhus, Rotavirus, Rubella, Measles, Mumps.

⭐ Sabin (oral polio) vaccine is a live attenuated vaccine; Salk (injectable polio) vaccine is killed. This distinction is crucial. )

Inactivated & Toxoid Vaccines - Neutralized Foes

  • Inactivated (Killed) Vaccines:
    • Whole or fractional pathogens, killed (heat/chemical). Cannot replicate.
    • Safer than live vaccines; generally suitable for immunocompromised.
    • Often require adjuvants & multiple doses (boosters).
    • Primarily humoral immunity (IgG).
    • Examples: Polio (Salk-IPV), Rabies, Hepatitis A, Influenza (inj.), Pertussis (wP/aP), Cholera (inj.), Typhoid (inj. ViPS), JE (inactivated).
  • Toxoid Vaccines:
    • Bacterial toxins inactivated with formalin (toxoids).
    • Immunity against toxin action, not organism.
    • Require multiple doses; good stability.
    • Examples: Tetanus (TT), Diphtheria (DT, Td).

    ⭐ Tetanus Toxoid (TT) and Tdap are recommended during each pregnancy to protect the newborn from tetanus and pertussis. Types of Vaccines Overview

Subunit & Newer Vaccines - Smart Shots

  • Subunit Vaccines: Purified antigenic parts, not whole organisms.
    • Pros: ↑Safety, ↓reactogenicity.
    • Cons: May need adjuvants, multiple doses; potentially lower immunogenicity.
    • Types & Examples:
      • Protein: Hepatitis B, Acellular Pertussis.
      • Polysaccharide: Pneumococcal (PPSV23), Typhoid Vi.
      • Conjugate (Polysaccharide + Protein): Hib, PCV, Meningococcal. 📌 Conjugation Converts for Children.

        ⭐ Conjugation converts T-independent polysaccharide antigens to T-dependent, improving immunogenicity, especially in infants <2 years.

  • Newer Vaccine Platforms:
    • mRNA Vaccines: (e.g., COVID-19: Pfizer, Moderna)
      • mRNA in lipid nanoparticles → host cells produce antigen.
      • Rapid development, high efficacy.
    • Viral Vector Vaccines: (e.g., COVID-19: AstraZeneca, Sputnik V; Ebola)
      • Non-replicating/attenuated virus delivers antigen gene.
    • DNA Vaccines: Plasmid DNA introduced → antigen production by host cells. (Mainly research/veterinary)

Vaccine mechanisms and immune response

High‑Yield Points - ⚡ Biggest Takeaways

  • Live attenuated vaccines: Strong immunity, risk reversion; avoid in immunocompromised & pregnancy.
  • Killed/Inactivated vaccines: Safer, need multiple doses & boosters; primarily humoral immunity.
  • Toxoids (e.g., Tetanus, Diphtheria): Inactivated bacterial toxins; require boosters.
  • Subunit vaccines: Polysaccharide poor under 2 years; Conjugate effective in infants. Recombinant (e.g., Hep B) by genetic engineering.
  • mRNA & Viral Vector vaccines: Newer platforms for rapid antigen delivery and immune response.

Practice Questions: Types of Vaccines

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Which of the following vaccines is classified as a killed vaccine?

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Flashcards: Types of Vaccines

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What is the duration of validity of 17D vaccination?_____

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What is the duration of validity of 17D vaccination?_____

Lifelong

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