Lecture 20: Vaccination Flashcards
What is a vaccine?
Something that stimulates the immune system, without causing serious harm or side effects
What is the aim of immunisation?
To provoke immunological memory to protect individual against a particular disease if you later encounter it
What makes a vaccine ideal?
- safe
- easy to administer
- single dose, needle-free
- cheap
- stable
- active against all variants
- life-long protection
What is significant about immune memory?
Movement to peak immune system response is much faster and stronger in second encounter of particular pathogen
Outline the principles of vaccination.
- expose immune system/naïve immune cells to antigen
- primary expansion of effector cells (clonal expansion)
- contraction (no. effector cells decreases, put into memory)
- second encounter = secondary expansion of effector cells (much faster and stronger)
How do vaccines stop infection?
1) Stops virus or bacteria getting into host cells - antibodies block entry, macrophage engulfs pathogen
2) Enables killing of infected cells - CD8+ killer T cells, T cells clear infected cells
3) Boosts immune responses - boosting CD4+ helper cells
How does clonal expansion of B cells lead to a highly specific antibody for the foreign antigen?
The B cell already made by our body that produces antibodies that best recognise the foreign antigen is the B cell that is selected to expand i.e. the better B cells survive (affinity maturation)
What is R0?
Basic reproduction number - no. cases one case generates on average over course of infectious period
What does it mean if R0 <1?
Infection will die out in long run
What does it mean if R0 >1?
Infection will be able to spread in a population
What will an effective vaccine do to R0?
Bring R0 to below 1
What is the principle behind herd immunity?
The more immune individuals there are, the less likely it is that a susceptible person will come into contact with someone who has the disease
What’s in a vaccine?
- antigen (could be in one of a variety of forms)
- adjuvant (normally alum), sometimes something proprietary
- stabilising stuff (e.g. buffers - PBS)
- water
What forms could antigen be in within a vaccine?
- inactivated protein e.g. tetanus toxoid
- recombinant protein e.g. Hep B
- Live attenuated pathogen e.g. Polio, BCG
- Dead pathogen e.g. Split flu vaccine
- Carbohydrate e.g. S. pneumoniae
What are inactivated toxoid vaccines?
Chemically inactivated form of toxin
What is the mechanism of action of inactivated toxoid vaccines?
Induces antibody, antibody blocks toxin from binding the nerves
Formulin locks shape, makes it inactive
What are the advantages of inactivated toxoid vaccines?
Cheap, well characterised, safe, in use for many decades
What are the disadvantages of inactivated toxoid vaccines?
Requires good understanding of biology of infection, not all organisms encode toxins, tiny risk of failure to inactivate/impurities
What are recombinant protein vaccines?
Uses recombinant protein from pathogen - gene of one organism moved to another, looks same as pathogen
What is the mechanism of action of recombinant protein vaccines?
Induces classic neutralising antibodies
What are the advantages of recombinant protein vaccines?
Pure, safe, because low strain variation and human only host highly protective
What are the disadvantages of recombinant protein vaccines?
Relatively expensive, has not proved to be answer to all pathogens
What are conjugate vaccines?
Polysaccharide coat component is coupled to an immunogenic “carrier” protein
What is the mechanism of action of conjugate vaccines?
Protein enlists CD4 help to boost B cell response to polysaccharide
