L27 - Scientific Basis of Vaccines Flashcards
Define vaccine?
‘A biological substance that does not cause disease, which, when administered to the recipient, produces an adaptive immune response which provides protection against future disease’
What is Herd Immunity?
Herd Immunity
Occurs when a significant portion of a population becomes immune to an infectious disease and the risk of spread from person to person decreases: those who are not immune are indirectly protected because ongoing disease spread is very small.
What are the general principles of vaccines?
Induce correct TYPE of response
Induce response in RIGHT PLACE
Duration of protection
Age of vaccination
What are monotypic and polytypic pathogens?
Monotypic e.g. Measles is serologically monotypic. Surface antigens have remained the same to date. Vaccination or infection gives lifelong immunity.
Polytypic e.g. Influenza. Surface antigens change and immunity is readily overcome
Describe the live attenuated organism as a type of vaccine?
serial culture in foreign host ‘passage’ e.g. Measles: 10 years of serial passage in tissue culture to transform wild virus into attenuated vaccine virus
chemical mutagenesis and selection of phenotypes e.g Salmonella typhi TY21a
genetic engineering to create knockouts lacking genes for virulence e.g. Vibrio cholerae
What is an advantage of live attenuated vaccine?
Live attenuated vaccines can be useful for producing CTL memory cells as they can infect APCs
What is a disadvantage of live attenuated vaccine?
Polio (Sabin) some cases of polio caused by reversion to virulence (virulent virus in nappies !)
Live attenuated vaccines will usually require a cold chain (refrigeration) to keep them alive – adds to vaccine costs difficult in some parts of world
Describe the killed/inactivated whole organism as a type of vaccine?
Killed with heat or chemicals e.g. formalin or β-propiolactone
What is a disadvantage of killed whole vaccine?
Boosting often required
Describe the Sub-unit vaccines as a type of vaccine?
Sub-unit vaccines (individual components)
- proteins (often surface antigen e.g. Hep B) - toxoids (diphtheria; tetanus) - peptides (synthetic) e.g. M-001 Influenza vaccine being trialled - polysaccharide - poor antigens - conjugated to toxoids or outer membrane protein (e.g. Meningitis C; Hib;)
How can bacteria; toxins be used as vaccines?
Toxins can be inactivated with formaldehyde to create a toxoid which is still antigenic and non-toxic
this can be used as a vaccine. The body creates antibodies which provide protection
What are some disadvantages of using bacterial capsular polysacharrides as vaccines?
create Poor antigens
short term memory no T-cell immunity
Much less immunogenic in children <2yrs
How can protein conjugation be used with polysacharrides to enhance immunity?
protein carriers are usually diptheria or tetanus toxoids or outer membrane proteins from bacteria (e.g. N.meningitidis) which are conjugated to polysaccharide capsule
More effective because the peptides from the protein can be taken up by the B-cell. Proteins can be presented by MHC Class 2 by the B-cell, to CD4 T-cells. They can provide cytokines to the Bc-cell to enable much stringer response
What do Vaccine Adjuvants do and give an example of one?
enhance immune response to antigen
promote uptake and antigen presentation
stimulate correct cytokine profiles
e.g.
Aluminium salts (Alum) : form trapped particles (depot)
slow release of antigen
What is Passive Immunity?
Passive immunity: maternal transfer.
Treatment with antibody from another source: serum
Prophylaxis and/or treatment Rapid Short effect
