Vaccines Flashcards
Define immunisation
Immunisation – Process whereby person or animal is made immune or resistant to infectious disease
What is R0?
Basic reproductive rate
The number of people that one sick persn will infect, on average, is called R0
If R0 is reduced <1 then transmission is halted
What is herd immunity?
- Form of immunity that occurs when vaccination of a significant proportion of a population provides a measure of protection for individuals that are not immune.
- Herd Immunity Threshold
HIT = 1 -1/R0
Percentage of fully immune individuals required to stop the spread of disease
Describe the different types of immunity
Describe how the immune respone acts when in contact with a vaccine
- Vaccine is delivered and Antigen presenting cells (such as macrophages, dendritic cells) take up the antigen part of the infecting cells from the cell surface
- The Innate system responsible for detecting PAMPs (Pathogen Associated Molecular Patterns) and DAMPs (Damage Associated Molecular Patterns) and presenting them through Pattern Recognition Receptors(PRR) to APC
- APCs the present antigens from the infecting cells to naive T cells specific for that antigen, which recognises it as foreign and is activated. - This normally takes place in lymph nodes
- B cells become activated, with the help of T helper cells, and undergo cell division. Some develop into plasma cells, and others memory B cells
- Antibodies are released from developed plasma cells
- Antibodies:
- Neutralization of infectivity owing to binding of viral surface antigens
- Destruction of infected cells – antibody dependent cellular cytotoxicity. Macrophages and NK cells carrying Fc receptors bind to the antibodies.
For which type of vaccine is the T cell response important for?
If attenuated virus vaccine, then T cell response important in destroying infected cells
What is the goal of vaccination?
Goal of vaccination is to produce memory cells to the vaccine antigen
What happens post-vaccination if someone is exposed to the infection they have been vaccinated against? (in the immune response)
- Entry of pathogen activated memory T cells which encourage immune response
- Memory B cells become active plasma cells (more antibodies produced at a faster rate)
- Memory killer T cell response may be reactivated
What are protective antigens?
Protective antigens – one that can stimulate an immune response and prevent/alleviate the clinically important consequences of infection.
What are adjuvants?
Adjuvants – substances of various kinds that enhance immune response
- What are the two groups of vaccines?
- Name some of both
Non replicative (+/- adjuvant)
- Whole virion
- Split
- Subunit
- Pure antigen
Replicative
- Live attenuated
- Vectorised (gene of protective antigen introduced in a vector)
- DNA based
Describe an inactivated vaccine, pros, cons and some examples
- Inactivated vaccines are made of whole microorganism destroyed by heat, chemicals, radiation or antibiotics
- Examples = Influenza, cholera, polio
- Advantages
- Stable
- Constituents clearly defined
- Unable to cause the infection
- Disadvantages
- Need several doses
- Local reactions common
- Adjuvant needed
- keeps vaccine at injection site
- activates antigen presenting cells
- Shorter lasting immunity
Describe attenuated vaccines, pros, cons and examples
- Live organisms modified to be less virulent
- Examples: measles, mumps, rubella, yellow fever
- A number of methods used to achieve attenuation
- Naturally occurring (e.g. Poliovirus strain with lack of virulence for brain and spinal cord in monkeys.
- Adenovirus vaccine (types 4 and 7) given orally was restricted to replication in the GIT.
- Derived from wild type through serial passage in cell cultures prepared from an unnatural host. -> mutants partially restricted in humans at portal of entry and/or target organs.
- Advantages
- Single dose often sufficient to induce long-lasting immunity
- May stimulate response to multiple protective antigens
- Strong immune response evoked
- Local and systemic immunity produced – particularly important for infections where CMI plays an important role. Activation of all components of immune system
- Disadvantages
- Potential to revert to virulence
- Can cause illness directly
- Contraindicated in immunosuppressed patients
- Interference by viruses or vaccines and passive antibody
- Poor stability
- Potential for contamination
What are toxoid vaccines and some examples?
- Vaccine made of inactivated toxic components
- Examples: tetanus and diptheria
What are subunit vaccines and some examples?
- Protein component of the microorganisms or synthetic virus like particles.
- Lacking viral genetic material and unable to replicate.
- Examples:
- Hepatitis B, HPV
What are conjugate vaccines and some examples?
- Poorly immunogenic antigens paired with a protein that is highly immunogenic (adjuvant)
- Examples:
- Haemophilus influenzae type B
What are heterotypic vaccines and some examples?
- Pathogens that infect other animals but do not cause disease or cause mild disease in humans
- Examples:
- BCG
What are some common components of vaccines?
- Active Component/Antigens
- Stabilizers
- Help maintain effectiveness during storage
- Factors affecting stability – Temperature, pH
3.Adjuvants
•Highly heterogeneous group of compounds with the ability to enhance immune response
4.Preservatives
- Particularly in multidose vaccines to prevent bacterial and fungal growth
- E.g. Thiomersal
5.Antibiotics
- (In trace amounts) Used during manufacturing phase to prevent bacterial and fungal growth
- E.g. MMR <25micrograms of neomycin
6.Trace components
- Formaldehyde – used to inactivate viruses and detoxify bacterial toxins
- A purification process during production removes almost all formaldehyde
Describe the contraindications and precautions of the following vaccines
- All
- DTP
- Influenza
- Live vaccines
What are some serious reactions that the following vaccines can cause?
What is needed for successful disease eradication?
- No animal reservoir
- Antigenically stable pathogen with only one (or small number of) strains
- No latent reservoir of infection and no integration of pathogen genetic material into host genome
- Vaccine must induce a lasting and effective immune response
- High coverage required for very contagious pathogens
