Vaccination Flashcards
What is the main aim of immunisation?
To provoke immunological memory to protect individuals against a particular disease if they later encounter it.
What are the 7 key points of an ‘ideal vaccine’?
- Completely safe
- Easy to administer
- Single dose, needle-free
- Cheap
- Stable
- Active against all variants
- Life-long protection
What are the 3 ways vaccinations stop infections upon second exposure?
- Prevention of entry - antibodies specific to the pathogen bind and block entry
- Killing infected cells - antibodies opsonise the pathogens
- Boosting immune response - Engages CD4 helper cells which enable both B cells and NK cells.
What are correlates of protection?
Measurable signs that a person is immune from a disease. Usually an ELISA assay is used to quantify antibody levels in blood and check whether it is above the threshold value for immunity.
What do correlates of protection enable?
- Allows for smarter vaccine design
2. Allows for smaller efficacy studies
How does BCR selection occur?
B cell antigen specificity is determined by the surface bound BCR antibody. It has a light and heavy chain encoded by individual genes made by recombination of building blocks.
What is affinity maturation?
Tfh cells present a very small amount of antigens in the lymph node. B cells undergo small point mutations in the BCR gene to improve specificity. B cells that can bind to the antigen are selected for.
Why do people have multiple rounds of vaccination?
Improves specificity of BCR due to repeated exposure to antigen.
What is r0?
This is the basic reproduction number and refers to the number of cases on case generates over the course of the infectious period. For example if the r0 value is 3 then 1 infected person will infect 3 others on average.
Any r0 above 1 will spread through the population. A good vaccine will bring the r0 value below 1.
What is herd immunity?
Reduces the amount of infectious spread without having to immunise every individual in a population. This is because if a significant proportion of the population is immune then there is a lower chance for a transmitting case to meet a susceptible individual compared to an immune individual. This immune individual will also not pass on the infection to a susceptible individual therefore the susceptible individual is protected.
What are the 5 forms of antigens present in a vaccine?
What else is present in 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.
Other:
Water, buffer, adjuvant
What are inactivated toxoid vaccines?
A chemically inactivated form of toxin is present in the vaccine that induces an antibody response e.g. tetanus toxoid.
Adv - Cheap, well characterised, safe, in use for many decades
Disadv - Requires good understanding of biology of infection and not all organisms encode toxin. There is also risk that the toxin is not properly inactivated.
What are recombinant protein vaccines?
Recombinant protein from pathogen induces classic neutralising antibodies e.g. Hep B surface antigen.
Adv - Pure, safe, low strain variation
Disadv - Relatively expensive and doesn’t work on all pathogens. For example the bacteria might have a carbohydrate capsule which is not very good at inducing a B cell response.
What are conjugate vaccines?
A polysaccharide coat component is coupled to an immunogenic carrier protein. The B cell binds to the polysaccharide part whilst antigen presenting cells such as dendritic cells bind to the protein part. However the B cell also presents the protein part on its MHC 2 molecules This means it can be activated by a T helper cell activated by the protein presented by the dendritic cell but produce antibodies specific to the polysaccharide. This improves the quality of the immune response.
Adv - Improves immunogenicity and is highly effective at controlling bacterial infection
Disadv - Expensive, carrier protein can interfere, very strain specific
What are dead pathogen vaccines?
The pathogen is chemically killed then inserted into the vaccine. This triggers antibody and T cell responses.
Adv - Leaves antigenic components intact and in context of other antigens. This makes it more immunogenic.
Disadv - Killing can slightly alter chemical structure of antigen. Requires capacity to grow the pathogen and there is a risk of contamination with live pathogen in the vaccine.
