Bacterial and Viral Vaccines Flashcards
What is R0?
The number of people one sick person will infect on average.
What is the R0 of hepatitis?
2
What is the R0 of ebola?
2
What is the R0 of HIV?
4
What is the R0 of SARS?
4
What is the R0 of mumps?
10
What is the R0 of measles?
18
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 is the percentage of fully immune individuals required to stop the spread of disease.
HIT = 1 -1/R0
How do vaccines trigger the immune response?
Antigen Presenting Cells present part of the antigen on the cell surface.
APCs present antigens to naïve T cells (in lymph nodes) which are activated.
Activation of B cells in response to antigens (+/- APCs).
Proportion of activated B cells will mature into plasma cells.
Plasma cells produce antibodies specific for the vaccine antigen.
How do antibodies and T cells neutralise pathogen activity?
Antibodies bind to specific antigen:
- Neutralization of infectivity
- Antibody dependent cellular cytotoxicity
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.
Response to pathogen post vaccination is increased and more antibodies are produced.
Why are vaccines less effective in elderly people?
Decreased resevoir of naive T-cells.
What are inactivated vaccines?
Whole microorganism destroyed by heat, chemicals, radiation or antibiotics (e.g. Influenza, cholera, polio).
What are the advantages of inactivated vaccines?
Stable
Constituents clearly defined
Unable to cause the infection
What are the disadvantages of inactivated vaccines?
Need several doses
Local reactions common
Adjuvant needed
Shorter lasting immunity
What are live attenuated vaccines?
Live organisms modified to be less virulent.
Examples: Measles, mumps, rubella, yellow fever
What are toxoid vaccines?
Inactivated toxic components.
Examples: Tetanus, diphtheria
What are subunit vaccines?
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?
Poorly immunogenic antigens paired with a protein that is highly immunogenic (adjuvant).
Examples: Haemophilus influenzae type B
What are heterotypic vaccines?
Pathogens that infect other animals but do not cause disease or cause mild disease in humans.
Example: BCG
What are viral vectored vaccines?
Use a modified virus (e.g. adenovirus) to deliver genetic code for an antigen.
Examples: Ebola, Janssen and AZ COVID vaccines
What are nucleic acid vaccines?
Use DNA/RNA from the pathogen.
Examples: Pfizer and Moderna COVID vaccines.
What are the components of a vaccine?
Stablisers
Adjuvants: Increase immune response without decreasing specificity
Preservatives
Antibiotics: Used to manufacture but subsequently removed
Trace components
What is the most common adjuvant used?
Aluminium hydroxide
Which vaccines are contraindicated in HIV patients?
Yellow fever
BCG
NOT MMR
How long should be left before primary doses of the same vaccine?
3 weeks to avoid competition
What are prerequisites for success for disease elimination?
- 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
What are determinants of primary vaccine antibody response?
Vaccine type:
- Live vs attenutated
- Protein vs polysaccharide
- Adjuvants
Antigen nature:
- Polysaccharide agents
- Protein antigens
- Antigen dose
Vaccine schedule:
- Interval between doses
- Genetic determinants
- Environmental factors
- Age at immunisation
What are determinants of duration of protection post immunisation?
Vaccine type:
- Live vs attenuated
- Polysaccharide antigens
Vaccine schedule:
- Interval between primary doses
- Interval between boosting
- Age at immunisation
- Environmental factors