Vaccination Flashcards
Define vaccine and aim of immunisation
Something that stimulates the immune system without causing serious harm or side effects. Aim of immunisation is to provoke immunological memory to protect individual against a particular pathogen if they later encounter it.
What are the qualities of an ideal vaccine?
- Completely safe
- Easy to administer
- Single dose, needle-free
- Cheap
- Stable
- Active against all variants
- Life-long protection
What does a vaccine generate?
Immune memory in the absence of harmful infection. Prevention of entry mediated through antibodies as they bind to virus and neutralise it so it never infects a cell. Antibody can lead to opsonisation of pathogen. Vaccine will be recognised by CD4 T cells in context of MHC 2 molecules which are programmed to boost other aspects of immune response eg. Activating CD8 T cells or B cells to form plasma cells.
What does R0 represent?
Basic reproduction number. If R0<1, infection will die out in long run whereas opposite if R0>1. Measures the number of cases one case generates on average over the course of their infectious period. R0 is liable to change depending on vaccination and population behaviour.
What is herd immunity?
In herd immunity, transmission is terminated or reduced as a transmitting case doesn’t meet a susceptible case and hence another transmitting case not created.
Describe development of vaccine types
Initially started with observation, led to attenuation (bacteria), then inactivation of the toxins, then a combination of inactivation and attenuation to target viruses, finally conjugation and now recombination.
What are the different forms of an antigen a vaccine can have? Provide examples
- Inactivated protein e.g. tetanus toxoid
- Recombinant protein e.g. Hep B surface antigen (HbSAg)
- Live Attenuated Pathogen e.g. Polio/BCG
- Dead pathogen e.g. Split Flu vaccine
- Carbohydrate e.g. S. pneumoniae
What are two other things vaccines contain and what is their purpose?
- Adjuvant – allows vaccine to work better, usually alum
* Stabilising e.g. buffers such as PBS
What is an inactivated toxoid vaccine? Adv and Disadv?
These are chemically inactivated form of the toxin. Induces antibody which blocks toxin binding nerves.
Advantages: Cheap, well characterised, safe, in use for many decades
Disadvantages: Requires good understanding of biology of infection, not all organisms encode toxins
What is a recombinant protein vaccine?
Recombinant protein from pathogen used to induce classic neutralising antibodies. Protein structure critical for recombinant protein vaccine and an example is RSV (mainly affects children and has a spike protein). It has a pre-fusion shape which changes to post-fusion once it enters the cell and that’s how virus injects material into cell. If you inject virus into people, antibodies made against post-fusion shape which is wrong so when virus actually enters body, the pre-fusion form in circulation will not be recognised by antibodies. Therefore, works well for protein surfaces.
What are the adv and disadv of a recombinant protein vaccine?
Advantages: Pure, safe
Disadvantages: Relatively expensive, not immunogenic, work better with adjuvant, doesn’t work against all pathogens
Why are bacterial coats uneffective and what is an alternate approach?
Bacterial coats not useful as often have polysaccharide capsule and not good at inducing B cell response. Instead, conjugate vaccines are useful as polysaccharide coat component is coupled to an immunogenic carrier protein which enlists CD4 help to boost B cell response to the polysaccharide. T cell recognises protein part while B cell recognises polysaccharide.
What are the adv and disadv of a conjugate vaccine?
Advantages: Improves immunogenicity, highly effective at controlling bacterial infection
Disadvantages: Cost, carrier protein interference, strain specific, polysaccharide alone poorly immunogenic
What is a dead pathogen vaccine? Adv and Disadv?
Is a chemically killed pathogen which induces antibody and cytotoxic T cell response.
Advantages: Leaves antigenic components intact and immunogenic due to inclusion of other components, cheap and quick
Disadvantages: Fixing/killing alters chemical structure of antigens, requires capacity to grow the pathogen, vaccine induced pathogenicity a risk, risk of contamination by live pathogen possible
What is a live attenuated vaccine? Adv and Disadv?
Pathogens attenuated by serial passage which leads to loss of virulence factor as they replicate in situ and hence trigger innate immune response plus boost immune response.
Advantage: Induce strong immune response, esp local in site where infection might occur.
Disadvantage: Can revert to virulence, can infect the immunocompromised, attenuation may lose key antigens, can be competed out by other infections if person already infected.
