Types of Vaccines

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.

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)

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.