4.11 - Vaccination Flashcards
1
Q
What is a vaccine?
A
- something that stimulates the immune system without causing serious harm or side effects
- the aim of the immunisation is to provoke immunological memory to protect individuals against a particular pathogen if they later encounter it
2
Q
What are the features of the ideal vaccine?
A
- completely safe
- easy to administer
- single dose, needle-free (higher chance people take)
- cheap
- stable (so can move between site of manufacture and site of administration properly)
- active against all variants
- lifelong protection
3
Q
How do vaccines stop infection?
A
- vaccination is the generation of immune memory in the absence of harmful infection
- prevention of entry of pathogen into cells through antibodies
- bind to virus and neutralise it to stop it from ever infecting cells in the first place
- opsonisation of the virus that leads to macrophages engulfing it - driven by Fc on AB - boosting immune response - antigens in vaccine will be recognised by CD4 T cells in context of MHC II –> these cells boost immune response e.g. train CD8 T cells to kill infected cells, working with B cells to make antibodies
- enables killing of infected cells
4
Q
What kind of intervention are vaccines?
A
Population, not individual
5
Q
What is R0?
A
- basic reproduction number
- the number of cases one case generates on average over the course of their infectious period
- if R0 < 1 the infection will die out in the long run
- if R0 > 1 the infection will be able to spread in a population
- R0 can change - depends on population behaviour
6
Q
How do vaccines reduce R0?
A
- more vaccinated people in the population
- less chance of an infected person meeting a susceptible unvaccinated individual to pass on the virus –> decreases R0
- herd immunity - when a large percentage of the population is vaccinated, it makes it harder for the virus to spread to susceptible individuals as they are protected indirectly by vaccinated individuals
7
Q
What is in a vaccine?
A
- antigen - in one of these forms:
1. inactivated protein e.g. tetanus toxoid
2. recombinant protein e.g. hep B
3. live attenuated pathogen e.g. polio / BCG
4. dead pathogen e.g. split flu vaccine
5. carbohydrate e.g. S. pneumoniae - adjuvant - normally alum, sometimes something proprietary
- stabilising stuff (buffers - PBS)
- water
8
Q
What are the five classes of vaccine used in the UK?
A
- inactivated toxoid vaccine
- recombinant protein vaccine
- conjugate vaccine
- dead pathogen vaccine
- live attenuated vaccine
9
Q
What is an inactivated toxoid vaccine?
A
- e.g. tetanus toxoid
- vaccine has a chemically inactivated form of toxin - no longer toxic
- vaccine induces antibody which blocks the toxin from binding to cells (nerves in tetanus case)
- advantages: cheap, well characterised, safe, in use for many decades
- disadvantages: requires good understanding of biology of infection, not all organisms encode toxins
10
Q
What is a recombinant protein vaccine?
A
- e.g. hep B surface antigen
- recombinant protein from pathogen
- the gene from one organism is isolated and moved into a different organism –> protein is mass produced
- induces classic neutralising antibodies that combine the protein and stop the virus getting into cells
- advantages: pure, safe
- disadvantages: relatively expensive, not very immunogenic, has not proved to be the answer to all pathogens (protein structure affects this)
11
Q
How does protein structure affect recombinant protein vaccine?
A
- e.g. RSV has a spike protein on its surface with two different forms - prefusion and postfusion (after it has bound to cell - this is how the virus injects its contents into cell)
- vaccines are made for the prefusion structure but the proteins in the vaccine lapse into the second structure, which if injected, will make the wrong-shaped antibodies so the body won’t be able to see the virus properly so you don’t get immunised against the virus
- this issue happens with many viruses and can be solved but you need to be aware of it
12
Q
What is the issue when it comes to bacteria with inactivated toxoid vaccines and recombinant protein vaccines?
A
- work well for protein antigens but bacteria often have a polysaccharide capsule surrounding them, not protein
- this is not good at inducing a B cell response (it is a T independent antigen)
- alternative approaches needed
13
Q
What is a conjugate vaccine?
A
- e.g. S. pneumoniae
- vaccine is a polysaccharide coat component that is coupled to an immunogenic ‘carrier’ protein i.e. a sugar molecule stuck to a protein molecule, which B cell recognises
- protein enlists CD4 help to boost B cell response to the polysaccharide
- DC engulfs the whole antigen and presents the protein part onto MHC II - a B cell takes up the polysaccharide
- TfH primed by DC through interacting with the DC’s MHC II presented peptide and then goes to the matching B cell and boosts it
- B cells produce anti-sugar antibodies
- advantages: improves immunogenicity, highly effective at controlling bacterial infection
- disadvantages: cost, carrier protein interference, very strain specific, polysaccharide alone is poorly immunogenic
14
Q
What is a dead pathogen vaccine?
A
- e.g. influenza split vaccine
- rather than using a single antigen, it is a chemically killed pathogen
- this induces antibody and T cell responses
- advantages: leaves antigenic components intact and in context of other antigen, immunogenic because of the inclusion of other components, cheap, quick
- disadvantages: fixing/killing can alter chemical structure of antigen, quite ‘dirty’, requires the capacity to grow the pathogen, vaccine induced pathogenicity a risk, risk of contamination with live pathogen
15
Q
What is a live attenuated vaccine?
A
- e.g. BCG, live attenuated influenza vaccine, OPV
- pathogens are attenuated by serial passage - leads to a loss of virulence factors = virus looks the same but cannot cause damage
- because they replicate in situ, they trigger the innate response and boost the immune response
- advantages: induce a strong immune response, can induce a local immune response in the site where infection might occur
- disadvantages: can revert to virulence, can infect immunocompromised, attenuation may lose key antigens, can be competed out by other infections
