Immunisation & public health

Question 1

What is herd immunity?

Answer 1

a theory - if there is enough people (95%), immune to a disease, = prevent spreading & infecting non-immunised /susceptible indiv. (5%) from disease

Question 2

List 5 scientific reasons why vaccination may not protect a fully vaccinated individual from a vaccine preventable disease? * (6)

Answer 2

• insufficient/ sub-optimal response in healthy subjects: none - low resp. ≠ little - none Ab
• Waning immunity: low titre of Ab or poor memory
• interference by unrelated, underlying infectious disease
• individuals must be spread at an even distribution
• antigenic shift & drift = change virulence of pathogen
• poor vaccine efficacy

Question 3

Briefly explain two of the reasons that could explain vaccination failure?

Answer 3

1. Fail to vaccinate appropriately (incomplete series of doses)
2. Actual vaccine failure: a) clinical = gets corresponding illness. b) immunological = fails to produce Ab

Question 4

Vaccine efficacy equation =

Answer 4

incidence(unvacc.) - incidence(vacc.)
_____________________________ x100
incidence(unvacc.)

*incidence= case/total

Question 5

Why could insufficient circulating antibodies against a particular pathogen lead to infection following secondary exposure to that organism?

Answer 5

Low Ab ≠ opsinise pathogen = infection

Question 6

What is the estimated Herd immunity threshold (HIT) for measles & pertusis?

Answer 6

92-94%

Question 7

What is the estimated Herd immunity threshold (HIT) for influenza?

Answer 7

33-50%

Question 8

If a childhood vaccine did contain foetal cell components from the manufacturing process, what possible unintended influence could an immune response to these components have for the host?

Answer 8

Foetal cells = contaminated by human protein = IR towards non-self human protein and not the Ag for the disease (Ab to non-self human proteins)

Question 9

What is one potential disadvantage of mixing multiple antigens from various different microbes into a single vaccine as far as an affect on the adaptive immune response?

Answer 9

• it may be too much for the immune system to handle
• may have an IR but have poor memory
• hard to target specific Ag (focus on responding to 1 Ag)