12
Acknowledgment of Country
The University of Newcastle acknowledges the traditional custodians: the Pambalong clan of the Awabakal people.
Respects paid to Awabakal Elders past and present.
Learning Objectives
Understand what a vaccine is.
Describe different types of vaccines.
Immunity to Virus Infection
Development of Immune Response: Recognizes antigens on the virus surface (structural proteins) and/or antigens from infected cells.
Sterilizing Immunity: Response required to eliminate the pathogen completely.
Humoral Immunity: Activates antibodies directed against accessible viral structures; more effective against external antigens compared to internal, non-structural proteins.
Significance of Antibodies: Useful diagnostically (e.g. identifying HIV infection through p24 capsid-core protein).
Infection Control Approaches
Aim to reduce pathogen spread and provide rapid treatment.
Includes:
Population Level: Education, vaccination, quarantine.
Cut-off Infection Route: Personal hygiene, public hygiene, insecticide, social distancing, lockdowns.
Protection of Susceptible Populations: Active/passive immunization strategies.
Vaccination Overview
Purpose: Induces or boosts long-term immunity against specific pathogens without prior disease exposure.
Particularly essential for diseases with severe symptoms or ineffective immune clearance.
Adaptive Immunity: Involves B cells (antibody production) and T cells (cellular immune response) to establish memory of the pathogen.
Mechanism of How Vaccines Work
Antigen Presentation: Vaccines introduce viral antigens, activating APCs (Antigen Presenting Cells).
B Cell Activation: Results in antibody production and formation of memory B cells.
T Cell Activation: Helps in antibody response and forms memory T cells.
Induction of Neutralizing Antibodies: Essential for protection against reinfection.
Vaccine Development Considerations
Understand the pathogen’s replication site and immune response needed.
Must ensure responses can clear the virus effectively where it causes disease.
Major Sites of Viral Infection
Respiratory and GI Tract Mucosal Surfaces: E.g., rhinovirus, influenza.
Mucosal Surfaces with Systemic Spread: E.g., polio, measles.
Direct Systemic Infection: E.g., via insect vectors for hepatitis B.
Limitations of Vaccines
Antibody/cell access to target antigens crucial.
Vaccination often generates responses against a single virus type.
Antigenic drift/shifts can reduce vaccine effectiveness, especially in RNA viruses.
Animal reservoirs can lead to the emergence of new viral strains.
Active vs Passive Immunization
Passive Immunization: Transfer of preformed antibodies (e.g., from mother to infant).
Active Immunization: Stimulation of the individual's immune system to produce antibodies.
Established Types of Vaccines
Live-attenuated vaccines: Weakened live pathogens.
Inactivated vaccines: Killed pathogens.
Purified subunit vaccines: Use selected pathogen molecules.
DNA vaccines: DNA encoding antigens is administered.
Viral vector vaccines: Utilize modified viruses to deliver DNA.
mRNA vaccines: Use mRNA to instruct host cells to produce antigens.
Attenuated Vaccines
Advantages: Close mimicry to natural infection; effective immunity.
Disadvantages: Risk of reversion to virulence, storage challenges, and potential disease in immunocompromised individuals.
Inactivated Vaccines
Immune response generally weaker and often requires boosters.
No risk of virus reversion; but failure in inactivation could lead to active infections.
Vaccine Examples
Polio Vaccine
Caused by poliovirus.
Two vaccination methods: Salk inactivated vaccine and Sabin oral attenuated vaccine.
Smallpox Vaccine
Eradicated disease through a successful vaccination program and no animal reservoir.
Influenza Vaccine
Seasonal quadrivalent vaccine updated annually based on circulating strains.
Combination of different H1N1 and H3N2 strains for effective coverage.
The University of Newcastle acknowledges the traditional custodians: the Pambalong clan of the Awabakal people. Respects are paid to Awabakal Elders past and present.
Learning Objectives
Understand the definition, significance, and function of a vaccine in modern medicine.
Describe various types of vaccines, their mechanisms, and their roles in immunity and disease prevention.
Immunity to Virus Infection
Development of Immune Response
The immune system recognizes antigens on the virus surface, which are specific proteins that elicit an immune response, as well as antigens derived from infected cells.
A two-pronged response occurs involving both humoral and cellular immunity.
Sterilizing Immunity
This refers to an immune response that completely eliminates the pathogen from the body, preventing any future infections. This level of immunity is crucial for certain virulent pathogens.
Humoral Immunity
Humoral immunity activates B cells, which are responsible for producing antibodies that bind to viral antigens to neutralize them. This is especially effective against extracellular pathogens found in bodily fluids.
Compared to B cell activation, T cell activation is more essential for addressing cells that have already been infected, particularly for intracellular pathogens and for destroying infected cells directly.
Significance of Antibodies
Antibodies serve essential diagnostic roles, for example, identifying infections like HIV through tests targeting the p24 capsid-core protein, a critical part of the virus structure.
Infection Control Approaches
The strategy involves multiple levels of intervention aimed at reducing the spread of pathogens and rapidly treating infected individuals.
Approaches include:
Population Level: Focus on public health education, widespread vaccination campaigns, and quarantine protocols during outbreaks.
Cut-off Infection Route: This encompasses practices such as personal and public hygiene measures, the use of insecticides, implementation of social distancing guidelines, and instating lockdowns during significant outbreaks.
Protection of Susceptible Populations: Active (vaccination) and passive (antibody transfer) immunization strategies are employed to protect vulnerable groups like infants and the elderly.
Vaccination Overview
The primary purpose of vaccination is to induce a protective immune response and establish long-term immunity against diseases without prior exposure to the disease itself.
This is particularly critical for diseases that present severe symptoms or have a high rate of morbidity and mortality, such as measles or rabies.
Adaptive immunity relies on both B cells, which produce antibodies, and T cells, which mount a cellular immune response. Together, they form the basis of immunological memory, which allows for faster and more effective responses to subsequent exposures to the same pathogen.
Mechanism of How Vaccines Work
Antigen Presentation: Vaccines introduce specific viral antigens to the immune system, which activate Antigen Presenting Cells (APCs) that process and present these antigens to T cells.
B Cell Activation: Activating B cells leads to the production of antibodies tailored to the introduced antigens and the formation of memory B cells capable of responding rapidly upon re-exposure.
T Cell Activation: Activated T cells not only contribute to the antibody response but also help in the activation of additional immune cells and the formation of memory T cells that remain vigilant for future infections.
Induction of Neutralizing Antibodies: Essential for providing protection against reinfection by preventing pathogens from entering cells or neutralizing their effects once inside.
Vaccine Development Considerations
A thorough understanding of the pathogen, including its replication site and the immune response required for effective clearance, is critical in vaccine development.
It is essential that the immune response elicited can effectively eliminate the virus precisely where it causes disease.
Major Sites of Viral Infection
2. Respiratory and GI Tract Mucosal Surfaces: These sites are common entry points for viruses such as rhinovirus and influenza.
4. Mucosal Surfaces with Systemic Spread: Some viruses, like polio and measles, can spread from these surfaces to the entire body.
6. Direct Systemic Infection: Certain viruses, such as hepatitis B, can infect individuals directly through insect vectors.
Limitations of Vaccines
The access of antibodies and cells to target antigens is critical for a vaccine's success.
Vaccines often generate responses directed against a singular virus type, which can limit effectiveness against diverse strains.
Antigenic drift and shifts, particularly in RNA viruses, can greatly reduce vaccine effectiveness over time, necessitating frequent updates and re-evaluations of existing vaccines.
The presence of animal reservoirs can facilitate the emergence of new viral strains, presenting further challenges to vaccination efforts.
Active vs Passive Immunization
Passive Immunization: Involves the transfer of preformed antibodies from one individual to another, such as from mother to infant through breastfeeding, providing immediate but temporary protection.
Active Immunization: Involves stimulating the individual's immune system to produce its own antibodies, offering long-lasting protection through immunological memory.
Established Types of Vaccines
2. Live-attenuated vaccines: These contain weakened pathogens that replicate without causing disease, offering robust immunity.
4. Inactivated vaccines: Comprising killed pathogens, these often require booster shots as the immune response is generally weaker.
6. Purified subunit vaccines: Focus on selected molecules from the pathogen, minimizing the risk of adverse effects associated with whole pathogens.
8. DNA vaccines: DNA encoding relevant antigens instructs host cells to produce these antigens for immune recognition.
10. Viral vector vaccines: Utilize harmless viruses to deliver DNA that encodes pathogen antigens.
12. mRNA vaccines: This innovative method uses messenger RNA to direct cells to produce antigens corresponding to the pathogen.
Attenuated Vaccines
Advantages: They closely mimic natural infections, leading to more effective and longer-lasting immunity compared to other vaccine types.
Disadvantages: Risks include potential reversion to a virulent form, challenges in storage and transport, and increased caution in administering to immunocompromised individuals, who might experience adverse effects.
Inactivated Vaccines
Generally elicit a weaker immune response and may require booster shots to maintain long-term protection.
They pose no risk of reverting to a pathogenic state; however, ineffective inactivation could lead to active infections, highlighting the importance of thorough testing during vaccine development.
Vaccine Examples
Polio Vaccine
Caused by poliovirus, polio vaccines have two vaccination methods: the inactivated vaccine (Salk vaccine) and the oral attenuated vaccine (Sabin vaccine). Both have effectively significantly reduced polio incidence globally.
Smallpox Vaccine
Smallpox was eradicated through an extensive vaccination program, demonstrating the potential success of vaccines when utilized effectively. It had no animal reservoir, which facilitated its elimination.
Influenza Vaccine
The seasonal quadrivalent influenza vaccine is updated annually, based on the circulating strains to maintain efficacy. It includes various combinations of H1N1 and H3N2 strains to provide effective coverage against the most common and virulent flu viruses.