W13L23 - Immunisation and Public Health

Question 1

Types of Vaccines

Answer 1

Whole organism
- killed vs live attenuated organisms
Antigen/component vaccines
- utilise/target specific virulence factors
Conjugate vaccines
- utilises a carrier protein

Question 2

What does the vaccine DTaP stand for?

Answer 2

Diphtheria
Tetanus
Acellular protein

Question 3

What are the 2 general expectations of immunisation?

Answer 3

1. Vaccination provides effective protection to recipients against the relevant pathogen
2. Immunisation of a population prevents contagious infectious diseases circulating within the community

Question 4

What is Herd immunity?

Answer 4

The resistance to the spread of a contagious disease within a population that results if a sufficiently high proportion of individuals are immune to the disease

Question 5

Herd Immunity Threshold

Answer 5

The estimated percentage of the population that needs to be immune to a contagious infectious agent so to prevent transfer of diseases to susceptible people
The percentage required varies according to the microbe
Basic reproduction number (Ro)
- the average number of secondary infectious cases that are produced by a single index case in a completely susceptible population

Question 6

Vaccine Efficacy

Answer 6

The proportionate reduction in disease in a vaccinated group

((Incidence in unvaccinated - incidence in vaccinated)/incidence in unvaccinated) x 100

Question 7

Vaccination Failure

Answer 7

Occurrence of a specific disease in an individual despite previous vaccination
2 categories
1. Failure to vaccinate appropriately
2. Actual vaccine failure
- clinical failure = vaccinated patient gets a corresponding illness
- immunological = vaccinated person fails to produce Abs or the designated immunological marker of immunity

Question 8

Causes of Vaccination Failure - Host Related

Answer 8

1. Defined immunodeficiency
   - due to diseases
   - due to treatments
   - due to hereditary disorders
2. Insufficient or sub-optimal immune response in healthy subjects
   - non and low responders
3. Waning immunity
   - poor immunological memory
   - age related senescence
4. Suboptimal health status at the time
   - nutrition/deficiencies
5. Interference by an unrelated, underlying infectious disease
6. Immunological interference
   - maternal IgG abs

Question 9

Effect of Concurrent Illness/Co-infection on the IR

Answer 9

May prevent adequate immune response to secondary infection or antigenic challenge
One of the reasons why vaccine should not be delivered during any concurrent illness
E.g. mice infected with measles were more susceptible to Listeria monocytogenes

Question 10

Causes of Vaccine Failure - Vaccine Related

Answer 10

1. Vaccine antigens not 100% efficacious
2. Incomplete coverage of target organism
   - serotypes
   - strains
   - antigenic variants
3. Antigenic interference
   - interactions between co-administered vaccines/antigens
4. Infection caused by a vaccine strain of an organism
   - e.g. polio, measles, rubella
5. Manufacturing related problem
   - quality defect
   - batch variation

Question 11

Waning Titres of Antibody

Answer 11

Length of memory varies according to particular antigen/vaccine components
- Tetanus = 1 shot every 10 years
- Pertussis = 1 shot every 4-10 years
The problem of low numbers of circulating antibodies
- insufficient Abs = inability to opsonise pathogen
Waning Abs titres not always a problem as long as the pathogenesis of an infection is slower than the secondary humoral immune response

Question 12

Antigenic Mismatch

Answer 12

The antigen(s) used in te vaccine are different to the antigen(s) present on microbial pathogen responsible for particular infection 
E.g. the vaccine for influenza type B will not give significant protection against infection from influenza types A, C, D etc