Vaccination (20) Flashcards
What is a vaccine?
stimulates the immune system without causing serious harm or side effects
e.g. purified viral protein, killed bacteria
What is the aim of immunisation?
to provoke immunological memory to protect an individual against a particular disease if they later encounter it
What characteristics are in an ideal vaccine?
- completely safe
- easy to administer
- cheap
- single dose, needle-free
- heat stable
- active against all variants
- lifelong protection
How does a immune memory decrease the response time to a pathogen?
- on first encounter (primary response), takes days to develop
- on repeat infections (secondary response), is faster and stronger
How do vaccines stop infection?
- prevention of entry: antibodies produced by B cells and macrophages engulf
- killing infected cells: killer T cell response (CD8)
- boosting immune response: CD4 helper T cells
What are correlates of protection?
- measurable signs that a person is immune, in the sense of being protected against becoming infected and/or developing disease
- antibody often used
- enable smaller efficacy studies and smarter vaccine design
What is clonal selection of B cells?
B cell that recognises the antigen is selected from the pre-existing cell pool of differing antigen specificities and then reproduced to generate a clonal cell population that eliminates the antigen
What determines B cell antigen specificity?
the BCR (B cell receptor)- has surface bound antibody and light and heavy chain, each encoded by an individual gene- made by recombination of building blocks (occurs in bone marrow before B cell released)
What are the 3 different pathways a B cell can take after antigen exposure?
- antibody production: become a plasma cell that produces antibodies
- affinity maturation: undergo a small amount of point mutations to change specificity of BCR–> make better at binding antigen…creates selective pressure on B cells
- memory: lay down memory B cells
What is R0?
- the basic reproduction number- number of cases one case generates on average over the course of their infectious period
- e.g. flu R0=1.3
- if R0<1 the infection will die out in the long run
What is in a vaccine?
antigen in the form of:
- 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
also an adjuvant (e.g. alum), some stabilising material and water
What are inactivated toxoid vaccines?
e.g. tetanus toxoid
chemically inactivated form of toxin–> induces antibody, antibody blocks toxin from binding
- cheap, well characterised, safe, in use for many decasdes
- but requires good understanding of biology of infection, not all organisms encode toxins, tiny risk of failure to inactivate
What are recombinant protein vaccines?
e. g. hep b surface antigen
- isolated surface antigen gene from virus is inserted into yeast–> modified yeast cells produce antigen, so looks the same but not infectious–> induces classic neutralising antibodies
- pure and safe, but relatively expensive and has not worked for all pathogens
Why are bacteria not very good at inducing a B cell response?
they often have a capsule made of polysaccharide
What are conjugate vaccines?
e. g. S pneumoniae
- stick polysaccharide onto carrier protein
- protein enlists CD4 to help boost B cell response to polysaccharide (conjugation allows T cell help)
