Comprehensive Notes on Immunization and Vaccination

Comprehensive Notes on Immunization and Vaccination 1. Basic Concepts of Immunization Immunization is the process of administering a vaccine to stimulate the body's immune system to recognize and fight pathogens, thereby preventing disease. Vaccination aims to reduce morbidity and mortality by generating protective immunity at both individual and community levels. Immune Response: A reaction of the body against a foreign agent (antigen) that helps eliminate pathogens and develop memory. Antigen: Any foreign substance that triggers an immune response, including viruses, bacteria, or their components. 2. Types of Immunity Innate Immunity • Present from birth; non-specific defense mechanism. • Includes barriers like skin, mucous membranes, phagocytic cells, and inflammatory responses. Adaptive Immunity • Antigen-specific defense mechanism developed after exposure to pathogens. • Includes two arms: cell-mediated and humoral immunity. Cell-Mediated Immunity • Involves antigen-specific cytotoxic T cells. • Essential for eliminating infected or abnormal cells. Humoral-Mediated Immunity • Involves B cells producing antigen-specific antibodies. • Provides long-lasting protection through immune memory. Immune Memory • Ability of the immune system to remember past infections or vaccinations. • Enables faster and stronger responses upon subsequent exposures. 3. Herd Immunity • Occurs when a sufficient proportion of the population is immune to a disease, reducing its spread. 1 • Basic Reproduction Number (R₀): Average number of secondary infections from a single infected individual. • R₀ > 1: Infection spreads, potential outbreak. • R₀ = 1: Disease becomes endemic. • R₀ < 1: Disease dies out. • Herd Immunity Threshold (HIT): Proportion of the population that must be immunized to stop spread. HIT = 1 - 1/R₀ • Measles: R₀ = 15-18; HIT = 93-95% • Smallpox: HIT = 80-85% 4. History of Vaccination • Edward Jenner (1796): Developed first smallpox vaccine using cowpox material. • Louis Pasteur (1885): Developed laboratory-produced rabies vaccine. • 1930s: Introduction of viral vaccines including yellow fever and influenza. • Modern advances include recombinant DNA vaccines and mRNA vaccines. 5. Types of Immunization Active Immunization • Administration of antigens to elicit protective immunity. • Natural Active: Infection with disease (e.g., COVID-19). • Artificial Active: Administration of vaccines. Passive Immunization • Transfer of pre-formed antibodies. • Natural Passive: Maternal antibodies through serum or milk. • Artificial Passive: Immune serum injection. 6. Sources of Antigens for Vaccines • Whole organisms (live, attenuated, or killed). • Toxoids (inactivated toxins). • Subunit antigens (surface proteins, polysaccharides, peptides). • Recombinant DNA or RNA constructs (e.g., COVID-19 vaccines). 7. Types of Vaccines Live, Attenuated Vaccines • Contain weakened pathogens capable of replication. • Examples: MMR, varicella, rotavirus. • Advantages: Strong, long-lasting immune response. • Risks: Not suitable for immunocompromised; rare reversion to virulent form. • Storage: Sensitive to heat and light. 2 Inactivated Vaccines • Contain killed organisms. • Examples: Hepatitis A, rabies. • Require higher doses or boosters; mostly antibody response. Subunit Vaccines • Contain specific antigenic components. • Examples: Pneumococcal conjugate vaccine. • Often conjugated to proteins for long-lasting immunity. Toxoids • Inactivated bacterial toxins. • Examples: Diphtheria, tetanus. • Require booster doses for prolonged protection. Recombinant Vaccines • Genes encoding antigens expressed in vectors. • Examples: Hepatitis B, HPV, influenza, COVID-19. • Advantages: Safer, consistent, and scalable. 8. COVID-19 Vaccines • ZyCoV-D: DNA vaccine with plasmid pVAX-1 expressing spike protein; intradermal delivery. • AstraZeneca-Oxford: Viral vector vaccine using replication-deficient chimpanzee adenovirus. • Pfizer BNT162b2: mRNA vaccine encoding spike protein; lipid nanoparticle delivery. • Spikevax Bivalent Original/Omicron: mRNA vaccine targeting original and Omicron BA.1 spike proteins. 9. Vaccine Production Techniques Traditional Methods • Egg-based production for influenza. • Cell-based production reduces mutations and scales rapidly. • Inactivation using chemicals (formaldehyde, glutaraldehyde). • Addition of stabilizers, adjuvants, and preservatives. Recombinant DNA Technology • Genes encoding antigens cloned into vectors. • Produces targeted immune response with reduced risk. • Used in Hepatitis B, HPV, and COVID-19 vaccines. 10. Influenza Vaccine Composition • Trivalent: 2 Influenza A strains (H1N1 + H3N2) + 1 Influenza B strain. 3 • Quadrivalent: 2 Influenza A strains + 2 Influenza B strains (B/Yamagata + B/Victoria). • Strains selected annually by WHO's GISRS network. 11. Vaccine Quality Control and Regulation • Testing for purity, potency, and safety. • Approval by national regulatory agencies. • Post-market surveillance to monitor effectiveness and safety. 12. Distribution and Vaccination Campaigns • Ensuring cold chain maintenance. • Annual influenza vaccination campaigns. • Public health programs to increase coverage and achieve herd immunity. 13. Features of Effective Vaccines • Safe, potent, immunogenic. • Long-lasting immunity. • Easy to produce and administer. • Suitable for target population. 14. Role of Pharmacists • Proper storage and handling of vaccines. • Patient counseling and education. • Promoting vaccination adherence. • Maintaining records and monitoring adverse events. 15. Summary Vaccination is a cornerstone of public health, utilizing a variety of strategies to induce immunity and prevent infectious diseases. From classical live-attenuated and inactivated vaccines to modern recombinant DNA and mRNA vaccines, immunization strategies continue to evolve. Achieving high coverage, understanding herd immunity, and ensuring vaccine safety are critical to successful disease control. 16. References • Plotkin SA, Orenstein WA, Offit PA. Vaccines, 7th Edition. • WHO. Immunization, Vaccines and Biologicals. • CDC. Vaccine Types and Production Methods. • Krammer F. SARS-CoV-2 vaccines in development, Nature, 2020. • UpToDate: Vaccination and Immunization Overview. 4