9.2 Principles of vaccination

Vaccination is a powerful tool in preventing infectious diseases. It works by introducing harmless versions of pathogens to stimulate our immune system, creating long-lasting protection without causing illness. This mimics natural infection but without the risks.

Vaccines activate our immune system in several ways. They trigger antigen presentation, T and B cell activation, cytokine production, and memory cell formation. Adjuvants are often added to boost these responses, making vaccines more effective at creating immunity.

Principles of Vaccination

Concept and goals of vaccination

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• Vaccination introduces antigenic material stimulating adaptive immunity mimicking natural infection without causing disease (polio vaccine)
• Goals prevent infectious diseases inducing long-lasting protective immunity reducing morbidity and mortality rates (smallpox eradication)
• Herd immunity provides indirect protection for unvaccinated individuals achieved when significant population immune (measles)
• Types of vaccines include live attenuated inactivated subunit toxoid and conjugate vaccines (MMR BCG flu shots)

Immune system activation by vaccines

• Antigen presentation involves uptake of vaccine antigens by APCs processing and presenting on MHC molecules (dendritic cells)
• T cell activation occurs through recognition of presented antigens by T cell receptors with co-stimulatory signals from APCs (CD4+ T cells)
• B cell activation happens via direct recognition of vaccine antigens T cell-dependent and T cell-independent activation (antibody production)
• Cytokine production stimulates immune cell proliferation and differentiation (IL-2 IFN-γ)
• Memory cell formation generates long-lived memory B and T cells providing rapid response to future infections
• Antibody production results from plasma cell differentiation and secretion of specific antibodies (IgG IgA)

Importance of vaccine adjuvants

• Adjuvants boost immune response to vaccines prolonging antigen release recruiting immune cells enhancing presentation (alum)
• Mechanisms include depot effect immune cell recruitment and activation enhanced antigen presentation
• Types comprise aluminum salts oil-in-water emulsions and TLR agonists (AS03 CpG)
• Benefits include increased antibody titers enhanced T cell responses and dose-sparing effect
• Considerations involve safety profile compatibility with specific antigens and target population factors (age immune status)

Challenges in vaccine development

• Antigenic variation complicates development due to rapid mutation of surface antigens and strain diversity (influenza HIV)
• Immune evasion mechanisms pose challenges for intracellular pathogens and those suppressing immune responses (tuberculosis)
• Complex life cycles with multiple stages or forms expressing different antigens complicate vaccine design (malaria)
• Lack of natural immunity in recovered individuals hinders vaccine development for certain pathogens
• Safety concerns include risk of vaccine-induced disease and autoimmune reactions (RSV)
• Technical challenges involve difficulty in culturing or producing antigens and maintaining stability during storage
• Ethical and logistical issues arise in clinical trial design implementation distribution and administration across diverse populations