Principles of Vaccination and Immunity

Principles of Vaccination

• Vaccination is the process of eliciting a long-lived state of protective immunity against a disease-causing pathogen.
• Exposure to a live pathogen, followed by recovery, is a natural form of immunization.

Immunity

• Immunity is the body's ability to tolerate its own material ("self") and eliminate foreign material ("non-self").

Types of Immunity

Passive Immunity

• Preformed antibodies are transferred to a recipient, often occurring naturally when maternal IgG crosses the placenta or through injection of preformed antibodies.
• Homologous pooled human antibody (immune globulin): Combined IgG from many donors, used in prophylaxis for hepatitis A and measles.
• Homologous human hyperimmune globulins: Antibody products with high titers of specific antibodies, used against hepatitis B, rabies, and tetanus.
• Heterologous hyperimmune serum (antitoxin): Produced in animals (usually horses), containing antibodies against a single antigen. Used to treat botulism and diphtheria.
• Monoclonal antibody: Produced from a single B cell clone, targeting a singular antigen or closely related group. Used in cancer treatment (chronic lymphocytic leukemia), transplant rejection prevention, and autoimmune disease treatment (rheumatoid arthritis).

Active Immunity

• Active immunity stimulates the immune system to produce antigen-specific antibodies.
• Unlike passive immunity, active immunity often lasts for many years.
• The persistence of protection is known as immunologic memory.

Vaccines

• Vaccines are biological preparations derived from living organisms and designed to enhance immunity to diseases.
• They can be prophylactic (preventative) or therapeutic (treating).
• Vaccines interact with the immune system to produce an immune response similar to a natural infection, without the risk of the disease.

Types of Vaccines

Live Attenuated Vaccines

• Microorganisms are weakened so they lose disease capability but still replicate.
• Jenner's smallpox vaccine is an example.
• Attenuation often involves growing the pathogen under atypical culture conditions.
• Example: Bacillus Calmette-Guérin (BCG).
• Advantages: Induce cell-mediated responses, typically requires a single dose.
• Disadvantages: Potential for reversion to a pathogenic form, must be handled safely.

Inactivated Vaccines

• The pathogen is killed using heat or chemicals.
• It cannot replicate but still induces an immune response.
• Examples include the Salk polio vaccine.
• Safety profiles tend to be higher than live attenuated vaccines.
• Often require multiple boosters to achieve full protection.
• Mostly induce humoral immunity (antibody response)

Subunit Vaccines

• Contain only specific, purified macromolecules from the pathogen (e.g., antigens).
• Examples include inactivated exotoxins (toxoids), capsular polysaccharides, and recombinant protein antigens.
• Provide protection against the disease without the whole microorganism.

Toxoid Vaccines

• Derived from inactivated bacterial toxins.
• Induce the production of antitoxins which neutralize the effects of the toxins.
• Example: Tetanus and diphtheria vaccines.

Capsular Polysaccharide Vaccines

• Contain the polysaccharide capsule from bacteria.
• The capsule helps avoid immune system recognition.
• Coating with antibodies or complement enhances macrophage and neutrophil phagocytosis.
• Example: Streptococcus pneumoniae vaccine, and Neisseria meningitidis vaccine.

Recombinant Vector Vaccines

• Use attenuated viruses or bacteria as vectors.
• The vector is modified to carry genes encoding key antigens of pathogens.
• Replication within the host results in antigen production.
• Minimizes the chance of harmful reversion to a normal state .

DNA Vaccines

• Employ plasmid DNA encoding antigenic proteins.
• Delivered into the muscle and expressed inside the host.
• Can be beneficial for long-lasting immunity.
• May require booster shots for enhanced protection.