9.2 Principles of vaccination
2 min read•july 25, 2024
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)
- provides indirect protection for unvaccinated individuals achieved when significant population immune ()
- 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 ()
- 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 ( 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
Key Terms to Review (21)
Adverse effects: Adverse effects refer to unintended, negative reactions or side effects that can occur following vaccination. These effects can range from mild symptoms, like soreness at the injection site or a low-grade fever, to more serious complications, although severe reactions are rare. Understanding these effects is crucial for evaluating the safety and efficacy of vaccines in the context of immunization programs.
Antibody production: Antibody production is the process by which B cells, a type of white blood cell, create antibodies in response to antigens, which are foreign substances like pathogens. This process is crucial for the adaptive immune response, allowing the body to recognize and neutralize specific threats. Understanding how antibody production occurs involves knowledge about where B cells develop, their maturation processes, and how vaccinations can stimulate this production to enhance immunity against diseases.
Cell-mediated immunity: Cell-mediated immunity is a type of adaptive immune response that primarily involves T cells in recognizing and responding to infected or abnormal cells. This immune mechanism is crucial for defending against intracellular pathogens like viruses and certain bacteria, as well as for the elimination of cancerous cells. The activation and differentiation of T cells, the various subsets they form, and their roles in vaccination, histocompatibility, and transplant rejection are all important aspects of understanding how cell-mediated immunity operates.
Clinical trials: Clinical trials are systematic studies that evaluate the safety and effectiveness of new medical interventions, such as vaccines or drugs, in humans. These trials are crucial for determining how well a vaccine can elicit an immune response and provide protection against diseases. They follow a structured process, typically divided into phases, that ensures thorough evaluation before any treatment is approved for widespread use.
Conjugate vaccine: A conjugate vaccine is a type of vaccine that combines a weak antigen with a strong antigen to enhance the immune response against the weak antigen. This approach is particularly effective for targeting polysaccharide antigens found on the surface of certain bacteria, which are often poorly immunogenic on their own. By linking these polysaccharide antigens to a carrier protein, conjugate vaccines stimulate a stronger and more lasting immune response, improving protection against specific bacterial infections.
Edward Jenner: Edward Jenner was an English physician and scientist who is credited with developing the first successful smallpox vaccine in 1796. His groundbreaking work laid the foundation for modern immunology and vaccination practices, demonstrating how exposure to a less virulent virus could confer immunity to a more dangerous one. This pivotal discovery not only saved countless lives but also revolutionized the approach to disease prevention through vaccination.
Herd Immunity: Herd immunity is the protection of a population from infectious diseases when a sufficient percentage of individuals are immune, either through vaccination or previous infections. This concept is crucial because it not only helps protect those who are vaccinated but also shields individuals who cannot be vaccinated, such as infants or those with certain health conditions. Understanding herd immunity is essential for developing effective vaccination strategies and controlling outbreaks of diseases.
Immunization: Immunization is the process by which an individual's immune system becomes fortified against an infectious agent, typically through vaccination. It involves the administration of a vaccine to stimulate the production of antibodies and activate specific immune responses, thereby providing protection against future infections. This process not only protects individuals but also plays a critical role in controlling the spread of diseases within populations.
Immunization coverage: Immunization coverage refers to the proportion of a population that has received specific vaccinations within a given timeframe. High immunization coverage is critical for achieving herd immunity, which protects those who are unable to be vaccinated due to medical reasons or age. It also plays a vital role in controlling the spread of infectious diseases and minimizing outbreaks.
Inactivated vaccine: An inactivated vaccine is a type of vaccine that contains pathogens that have been killed or inactivated, rendering them unable to cause disease while still provoking an immune response. This type of vaccine is crucial in the field of immunization as it helps to build immunity without the risk of infection, making it an important strategy for protecting public health against infectious diseases.
Influenza: Influenza, commonly known as the flu, is a contagious viral infection that affects the respiratory system, caused primarily by influenza viruses types A and B. This infection can lead to severe illness and complications, particularly in vulnerable populations such as young children, the elderly, and individuals with certain health conditions. Vaccination is one of the key strategies used to prevent influenza and mitigate its impact on public health.
Live attenuated vaccine: A live attenuated vaccine contains a weakened form of the pathogen that causes the disease, which stimulates an immune response without causing the illness. These vaccines often provide long-lasting immunity and can stimulate both humoral and cellular immune responses, making them effective in preventing infectious diseases.
Louis Pasteur: Louis Pasteur was a pioneering French microbiologist and chemist known for his discoveries in the fields of vaccination, microbial fermentation, and pasteurization. His work laid the foundation for the germ theory of disease, which revolutionized medicine and established crucial principles of vaccination and infection control.
Measles: Measles is a highly contagious viral infection characterized by symptoms such as fever, cough, runny nose, and a distinctive red rash that typically appears several days after the onset of initial symptoms. The measles virus is spread through respiratory droplets and can lead to serious complications, making vaccination critical in preventing outbreaks and protecting public health.
Multivalent vaccine: A multivalent vaccine is a type of vaccine designed to immunize against multiple strains or types of pathogens, such as viruses or bacteria, in a single formulation. This approach helps provide broader protection and enhances the efficiency of vaccination programs by reducing the number of injections needed for comprehensive immunity.
Pentavalent vaccine: A pentavalent vaccine is a type of immunization that targets five different pathogens or antigens in a single dose. These vaccines are designed to provide broad protection against multiple diseases, often including combinations of viral and bacterial infections, which is crucial for effective immunization programs, especially in children.
Subunit vaccine: A subunit vaccine is a type of vaccine that contains only specific pieces of the pathogen, such as proteins or sugars, rather than the whole microorganism. This approach allows the immune system to recognize and respond to these key components without using live or inactivated pathogens, making it a safer option for immunization. Subunit vaccines can effectively stimulate an immune response and can also contribute to herd immunity when a large portion of the population is vaccinated.
Toxoid vaccine: A toxoid vaccine is a type of vaccine that uses a toxin produced by certain bacteria, which has been rendered harmless or inactivated, to stimulate an immune response without causing disease. These vaccines help the body to recognize and fight the toxin if it encounters it again, providing immunity against diseases caused by the toxins of bacteria, like tetanus and diphtheria.
Vaccine efficacy: Vaccine efficacy refers to the percentage reduction of disease incidence in a vaccinated group compared to an unvaccinated group under controlled conditions. This measure is crucial as it helps determine how well a vaccine works in preventing illness, and it plays a vital role in understanding the overall effectiveness of vaccination programs. The concept is closely related to the principles of vaccination and the impact of herd immunity, as higher efficacy rates can significantly contribute to reducing disease transmission within populations.
Vaccine hesitancy: Vaccine hesitancy refers to the reluctance or refusal to vaccinate despite the availability of vaccines. This behavior can stem from a variety of factors, including concerns about vaccine safety, mistrust in healthcare systems, or cultural beliefs. Understanding vaccine hesitancy is essential in promoting vaccination efforts, ensuring community health, and achieving the full benefits of immunization.
Vaccine platform: A vaccine platform refers to the underlying technology or method used to develop and produce vaccines. This concept encompasses various approaches, such as live-attenuated, inactivated, subunit, and mRNA platforms, each with its own mechanisms for eliciting an immune response. Understanding vaccine platforms is crucial for evaluating their safety, efficacy, and how they can be adapted for different pathogens.