Vaccination Flashcards
What is a vaccine?
Something that stimulates the immune system without causing serious harm
The aim of immunisation is to provoke immunological memory to protect an individual against a particular pathogen later in life
What are some properties of an ideal vaccine?
Completely safe
Easy to administer
Single dose
Ideally needle free
Cheap
Stable
Active against all variants
Life long protection
When was smallpox eradicated?
1979, after the heat stable vaccine was introduced In the 1940s
This saved about 300 million Lives
How do vaccines work?
Prevents infection - antibodies lock entry and cause opsonisation lading to phagocytosis
Killing infected cell
Boosting immune response - CD4 T cells work with CD8 and B cells to boost the immune response
What is R0?
Basic reproduction number
The number of cases one generates in average over the course of their infectious period
This value can change
Rt is like the altered version of the R0 ( eg with a vaccine)
What is herd immunity?
The transmitting cases may only meet immune people. This shields further people from the chain of infection
What forms of antigen might a vaccine contain?
Inactivated proteins (tetanus toxoid)
Recombinant protein (hep B)
Live attenuated pathogen (polio/BCG)
Dead pathogen (split flu vaccine)
Carbohydrate (s. Pneumoniae)
What does a vaccine contain?
Antigen (in whatever form)
Adjuvant (makes it work better), normally alum, sometimes something proprietary
Stabilising stuff (buffers - PBS)
Water
What are Inactivated toxoid vaccines?
Eg. Tetanus
Chemically inactive form of toxin
Induces antibody, antobody block toxin from binding to target site
Cheap, well characterised, safe, in usd for many decades
Requires good understanding of biology of infection, not all organisms encode toxins
What are recombinant protein vaccines?
Eg. Hep B surface antigen (HbSAg)
Recombinant protein from pathogen
Induces classic neutralising antibodies
Pure, safe
Expensive, not very immunogenic, has not proved to be the answer for all pathogens. Bacteria have polysaccharides on their surface not proteins
What are conjugate vaccines?
Eg. S. Pneumoniae
Polysaccharide coat component is coupled to an immunogenic “carrier” protein
Protein enlists CD4 help to boost B cell response to the polysaccharide
Improves immunogenicity, highly effective at controlling bacterial infection
Costs a lot, Carrier protein interference, very stain specific, polysaccharide alone is poorly immunogenic
What are dead pathogen vaccines?
Eg. Influenza split vaccine, polio
Rather than using a single antigen, it is chemically killed pathogen
Induces antibody and T cell response
Leaves antigenic components intact in context of other antigen. Immunogenic because of inclusion of other components, cheap, quick
Killing can alter the structure of antigen, quite “dirty”, requires capacity to grow pathogen, vaccine induced pathogenicity is a risk, risk of contamination with live pathogen
What are live attenuated vaccines?
Eg. BCG, OPV (polio)
Pathogens are attenuated by serial passage. This leads to a loss of virulence factors
Because they replicate in situ they trigger the innate response and boost the immune response
Induce a strong immune response. Can induce a local immune response In the site where the infection might occur
Can revert to virulence, can infect immune compromised people, attenuation may lose key antigens, can be competed out by other infections
What are adjuvants?
They induce some of the “danger signals” that activate dendritic cells to present antigen to T cells.
Alum is commonly used
Also ASO3 and MF59
Why may we need new vaccines?
Changing (ageing) demographics
Changing environment
New diseases
Old diseases we still can’t fix
Antibiotic resistance
