Principles of Immunization

Immunization Fundamentals - Immunity 101 Kickstart

• Immunization: Process inducing immunity against specific diseases, primarily via vaccination.
• Immunity: Body's defense against pathogens. Two main types: Active & Passive.

• Active Immunity:
  • Host's immune system produces antibodies/cells after exposure to antigen (infection/vaccine).
  • Lag period: Yes (days to weeks).
  • Duration: Long-lasting (years/lifelong).
  • Memory: Present; subsequent exposure leads to faster, stronger response (booster effect).
• Passive Immunity:
  • Pre-formed antibodies are transferred to recipient.
  • Lag period: No (immediate protection).
  • Duration: Temporary (weeks to months, e.g., IgG half-life ~3 weeks).
  • Memory: Absent.

  ⭐ Artificially acquired passive immunity provides immediate but temporary protection (e.g., anti-tetanus serum).

Vaccine Arsenal - Types & Tactics

⭐ Live attenuated vaccines generally provide longer-lasting immunity and elicit a strong cell-mediated response, but carry a risk of reversion to virulence.

Vaccine Admin & Response - The Immune Tango

• Admin Routes: IM, SC, ID (BCG), Oral (OPV), Intranasal.
  • Site: Deltoid, anterolateral thigh (infants).
• Schedule: Primary series & boosters crucial.
• Cold Chain: ($+2$°C to $+8$°C) maintains potency.
• Immune Response:
  • Primary: IgM → IgG, memory cells.
  • Secondary (Anamnestic): Rapid, ↑IgG (memory).
• Factors Influencing Efficacy:
  • Vaccine: Type, dose, adjuvants.
  • Host: Age (extremes ↓), nutrition, immunity.

⭐ Adjuvants like aluminum salts (Alum) are used in some inactivated vaccines to enhance the immune response, particularly Th2 responses.

• Herd Immunity: Protects unvaccinated.

AEFI, Herd & Cold Chain - Beyond the Jab

• AEFI (Adverse Event Following Immunization): Any untoward medical event post-vaccination; not always causal. Crucial for safety surveillance.
  • Types: Vaccine product-related, quality defect, immunization error, anxiety-related, coincidental.
  • Serious AEFI: Death, life-threatening, hospitalization, persistent disability. Report promptly.
• Herd Immunity: Indirect protection of unimmunized when population immunity is high.
  • Threshold ($1 - 1/R_0$, where $R_0$ is basic reproduction number): Proportion immune needed. E.g., Measles >95%.
  • Protects vulnerable individuals (e.g., immunocompromised).
• Cold Chain: System ensuring vaccine potency via correct temperature storage/transport.
  • Temp: Most +2°C to +8°C. Freezer (e.g., OPV, Measles): -15°C to -25°C.
  • Vaccine Vial Monitor (VVM): Indicates cumulative heat exposure.
  • Heat sensitive: OPV, Measles, BCG. 📌 "Old Men Are Best" (OPV, Measles, BCG).
  • Freeze sensitive: DPT, TT, HepB, IPV. 📌 "Don't Touch The Ice Pack" (DPT, TT, HepB, IPV).

⭐ The cold chain is critical for maintaining vaccine potency, especially for live vaccines like measles and OPV, which are heat sensitive.

High‑Yield Points - ⚡ Biggest Takeaways

• Active immunity: Host immune response to antigen; long-lasting protection (e.g., post-vaccination).
• Passive immunity: Pre-formed antibodies transferred; immediate, temporary protection (e.g., maternal IgG).
• Herd immunity: Protects unvaccinated when population immunity is high, reducing pathogen spread.
• Live attenuated vaccines (MMR, OPV): Strong, often lifelong immunity; rare risk of reversion.
• Killed vaccines (IPV, Rabies): Safer, less immunogenic; require multiple doses/boosters.
• Adjuvants (Alum): Enhance immune response, especially for non-live/subunit vaccines.
• Anamnestic response: Faster, stronger, IgG dominant secondary immune response.