Lecture 31 - Vaccination I Flashcards
1
Q
Compare the terms vaccination and immunisation
A
- Vaccination: deliberate induction of immunity by administration of vaccine
- Immunisation: process by which an individual is made immune to a disease
- Vaccination leads to immunisation
2
Q
Compare the terms antigen and immunogen
A
- **Immunogen: **a molecule that induces an immune response
- **Antigen: **a molecule that is the target of an immune response
- Not all antigens are immunogens
3
Q
Who performed the first vaccination?
When?
How?
A
- Edward Jenner
- End of 1700’s
- Smallpox vaccination
- Observed that milkmaids did not die from smallpox
- Milkmaids exposed to cowpox (vaccinia) and developed immunity to it
- Hypothesised that immunity to cowpox prevented severe disease to smallpox (variola)
- Vaccinated James Phelps with vaccinia
- Boy protected from ‘repeated deliberate’ attempts to infect with Variola
- Observed that milkmaids did not die from smallpox
4
Q
Who characterised the mechanism of vaccination?
A
- Louis Pasteur, 1880’s
- Developed vaccines for:
- Rabies
- Anthrax
- By deliberately attenuating the organisms
- As opposed to Jenner, who had to find a less virulent form of the pathogen
- Vaccination with the attenuated form protected against the more virulent, wild type form
5
Q
What is the vaccine schedule?
A
- Schedule of the various vaccines that should be given to individuals at various ages
- Birth to 4 years: intensive schedule
- HepB
- Diphtheria
- Tetanus
- Poliomyelitis
- Rotavirus
- Pneumococcus
- H. influenzae
- Measles, Mumps, Rubella
- Varicella zoster
- etc.
- At risk groups:
- Aboriginal, Torres Strait Island populations
- Live in areas with endemic Pneumococcus
- Pregnant women
- Influenza
- Elderly:
- Influenza
- Pneumococcus
- Aboriginal, Torres Strait Island populations
6
Q
How do vaccines decrease disease in a population?
A
- Induce immunological memory: long lived immunity against a pathogen
- At the level of the individual
- eg. Diphtheria vaccine
- Provide herd immunity
- At the level of the population
7
Q
Describe immunological responses to vaccination
A
B cell responses
- Vaccination:
- Stimulates IgM and IgG (specific for antigen) production
- Low affinity initially, then higher affinity IgG
- Titre remains high over time
- Upon reinfection / boost:
- IgG levels rapidly increase to provide protection
T cell responses
- Vaccination:
- Stimulates generation of a T cell response
- Proliferation of the cells in the system
- Differentiation into various T cell subtypes
- Formation of a pool of memory cells
- Upon reinfection / boost:
- Memory cells rapidly are reactived
- Increased magnitude of response (compared to primary response)
8
Q
Describe herd immunity
A
Limitation of the ability of the pathogen to spread within a population
Only applies to diseases which are spread human-human
- Pathogens with a zoonotic origin can persist even after everyone is vaccinated
- Within a unvaccinated population:
- When one individual becomes infected with a pathogen, it will likely be transmitted to a number of other individuals
- Probability of coming across another unvaccinated individual is high
- The pathogen spreads
- Within a vaccinated population:
- When one individual becomes infected, it cannot be transmitted, as the others are vaccinated
- The spread of the pathogen is limited
- Chance of coming across another unvaccinated individual is low
9
Q
List factors that influence herd immunity
A
- Environmental factors
- Crowding
- Infectivity of disease
- Severity & symptoms
- If the symptoms are severe, the person is more likely to isolate themselves
- Sub-symptomatic disease: individual may still go to work etc. and spread the disease
- Severity & symptoms
- Rate of spread
- ie areas of high/low vaccine uptake
10
Q
Describe Ring Vaccination
A
Use of herd immunity to contain an outbreak
- Performed when it is not possible to vaccinate everyone
- Scenario:
- A particular community is infected
- Quarantine of infected individuals from non-infected
- Surrounding communities are vaccinated
- Prevents the spread of the pathogen to the surrounding communities
11
Q
What is Ebola?
Describe the 2014 Ebola outbreak
A
- Emerging, highly virulent virus
- 50% mortality rate
- Causes **viral **haemorrhagic fever
- Internal and external bleeding
- Ultimately leads to multiple organ failure
- 2014 outbreak:
- Outbreak in West Africa
- Sierra Leone, Guinea, Liberia
- Largest outbreak to date
- Currently 4,000 deaths
- Predicted 20,000 deaths by the end of the year
- Factors causing spread:
- No vaccine
- Still needs to be trialled for safety & efficacy, will take some time
- No accessible/viable treatments
- mAb therapy: expensive & difficult to manufacture
- Long incubation period → high transmissability
- 21 days from infection for the disease to manifest
- Mistrust
- Cultural practices
- Hygeine standards in these countries
- No vaccine
- This is a situation where ring vaccination would be beneficial
- Outbreak in West Africa
12
Q
Why are we seeing re-emergence of infectious diseases for which we have effective vaccines?
A
- Parents are not allowing their children to be vaccinated
- Because we don’t see infectious diseases in the first world, people think that there is no risk
- Through fear of autism from vaccination
- Herd immunity works when up to 95% of the population is covered
- Measles, Whooping cough
13
Q
What is an ‘ideal vaccine’?
A
Induces the same quality of immunity as would an infection with the natural pathogen
14
Q
What are adjuvants?
List a few
How do they work?
A
- Substance that hepls increase immunogenicity of a co-administered vaccine
- Some vaccines have low immunogenicity → adjuvant is required
- Others do not require them
- Examples
- Freunds complete adjuvant
- Very strong
- Toxic
-
Aluminium-based adjuvants
- Safe
- Adjuvant of choice for many clinically used vaccines
- Limited by ability to induce particular types of immune responses:
- Good neutralising Ab
- Poor cell-mediated responses
- Montanide water-in-oil formulations
- Good immunogenicity
- Freunds complete adjuvant
- MOA
- Stimulate pro-inflammatory responses
- Provide a depot of Ag
- Slow release of Ag
- Drawbacks
- Make simple concoctions more complex
15
Q
List some types of vaccine
Give examples of each
A
- Live attenuated
- Vaccinia
- BCG
- MMR
- Sabin poliovirus vaccine
- Inactivated
- Salk
- Various influenza subtypes
- Subunit
- HepB surface Ag (HBsAg)
-
H. influenzae type b
- Polysaccharide-protein conjugate
- Bordetella pertussis Ags
- Diphtheria toxoid
- Tetanus toxoid
