Scientific basis of vaccines Flashcards

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1
Q

State the definition of a (prophylactic) vaccine?

A

A biological substance that does not cause disease, which, when administered to the recipient, produces an adaptive immune response which provides protection against future disease

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2
Q

What considerations should be taken for vaccine development?

A
  • Protection (when + where)
  • Type of immune cells required
  • Site of immune response
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3
Q

Vaccine rationale
What can vaccines give protection to?

A
  • Individual (prevention or decrease of disease)
  • Populations (via herd immunity),
  • Eradiation of disease
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4
Q

Describe and explain herd immunity?

A
  • Majority of population are immune to disease
  • Risk of spread from person to person decreased
  • Those who are not immune are indirectly protected as ongoing disease spread is very small
  • % of people who need to be immune in order to achieve HI varies with disease.
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5
Q

Explain the vaccine paradox with herd immunity?

A
  • Herd Immunity memory boosted via periodic outbreaks of disease in community + vaccines
  • As diseases rate decreased - no natural boosting -> increased importance of vaccination uptake rates -> Vaccine uptake rate = reservoirs of infection = risk to population + individual -> epidemic (decreased VUR)
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6
Q

Principles of vaccines
Describe the primary and secondary responses to antigens?

A
  • Primary: 5-7 days - AB response -> 2 weeks for full response - IgM -> IgG switching + memory B + T cells
  • Secondary: (prior A exposure) - < 7 days for full response
  • Post exposure immunoprotection occurs -> response to specific antigens -> good targets for vaccines
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7
Q

State the general principles of vaccines?

A
  • Induce correct type of response
  • Response in right place
  • Duration of protection
  • Age of vaccination
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8
Q

Principles
State examples of the correct type of response principle for vaccines?

A

AB (polio) or cell mediated immunity (TB)

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9
Q

State examples of inducing response in the right place principle for vaccines?

A
  • Mucosal (secreted IgA - influenza)
  • systemic (yellow fever) -> Vaccines: parenteral (poor mucosal immunity)
  • Oral (mucosal)
  • Lymphoid tissue (MALT - good IgA production)
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10
Q

State examples of the duration of protection principle for vaccines?

A
  • Incubation period is the time elapsed between exposure to a pathogenic organism, a chemical, or radiation, and when symptoms and signs are first apparent.
  • Short term - AB sufficient
  • Long term - memory essential
  • Boosters - natural (seasonal epidemics, carriage)
    OR vaccines, type of infection
  • Long incubation time (systemic - measles)
  • Short incubation time (surface - cholera)
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11
Q

State examples of the age of vaccination principle for vaccines?

A
  • Maternal IgG AB enter foetus through placenta + slgA in breast milk -> provides weeks to months protection in neonate -> maternal AB may interfere with vaccine -> Optimum timing of vaccine determined via vaccination
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12
Q

Describe the difference between monotypic and polytypic pathogens and what type of immunity is involved with immunity?

A
  • Monotypic: surface antigens always remain same (measles) - single vaccinations = lifelong immunity
  • Polytypic: SA change + immunity readily overcome (antigenic drift) -> influenza
  • Antigenic drift: accumulation of mutations in genes that code for virus surface proteins with time
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13
Q

Type of vaccines
State the 4 types of vaccines?

A
  • Live Attenuated organism
  • Killed whole organism
  • Sub-unit
  • Conjugated
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14
Q

Describe how live, attenuated organisms are formed for vaccine use and state example of these?

A
  • ‘Passage’ (measles) -> serial culture in foreign host -> Organisms mutate + adapt to foregin host - decreased danger
  • Chemical mutagenesis + selection of harmless phenotypes -> salmonella typhi TY21a
  • Genetic engineering to create knockouts lacking genes for virulence (vibrio cholerae)
  • e.g. BCG, polio (sabin), MMR, yellow fever, VZV)
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15
Q

Describe problems behind using Live attenuated organisms as vaccines?

A
  • Vaccines pick up mutation - revert to virulence (polio)
  • Require cold chain (refrigeration) to keep alive -> increased cost
  • LA vaccines usefulness -> infect APC cells -> produce Tc memory cells
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16
Q

Killed whole-organism
Describe how a killed whole-organism is formed + features of its protective level compared with live attenuated?

A
  • Killed with heat or chemicals (formalin or B-propiolactone) -> e.g. pertussis, influenza, poilio (salk type), cholera, HA
  • Protective level: boosting often required -> LA vaccine has natural boosting via live organism
17
Q

Sub-unit
Describe the sub-unit vaccines and examples of these?

A

Individual components of pathogen used -> proteins (surface A - hep B), toxoids, peptides (synthetic), polysaccharide

18
Q

Describe the use of bacterial toxins as vaccines?

A

toxins - tissue damage + disease -> Convert to toxoids -> vaccine -> produces AB -> binds toxins - protect -> e.a. tetanus + diptheria

19
Q

Why may subunit vaccines need to be boosted?

A
  • Specific antigens may lack PAMPs (‹ danger signals),
  • immune response may only be AB-mediated, not cell-mediated -> immune response weaker than others -> Increase immune response = use adjuvants or boosters
20
Q

Define antigen drift and shift

A
  • Antigenic drift: Accumulation of mutations in genes that code for virus surface proteins with time
  • Antigenic shift: Recombination of viral strains to produce a different subtype with a mixture of surface antigens from the original strains
21
Q

Conjugated
Describe the use of bacterial capsular polysaccharides as vaccines?

A
  • Increased immunogenicity via protein conjugation (BCP + protein) -> protein carriers
  • diptheria or tetanus toxoids or outer membrane proteins from bacteria (e.g. N.meningitidis) which are conjugated to polysaccharide capsule
    -> long lasting immunity + response in children -> e.g. Neisseria meningitidis Group C, MenC vaccine, Haemophilus influenza Type B, Hib vaccine
22
Q

Why is bacterial capsular polysaccharides not good to use alone?

A
  • Poor antigens -> short term memory + no T-cell immunity
23
Q

Describe conjugation + how they work?

A
  • Link carrier protein with polysaccharide of bacteria -> Binds BCR -> presents protein + recognised via Th cell -> Cytokine release -> T helps B -> Increased immune response + good memory
24
Q

Vaccine adjuvants
What are vaccine adjuvants, their advantages + example?

A

Chemical added to vaccines
- immunogenic
- Increase immune response to antigens
- Increase uptake + antigen presentation
- Stimulate correct cytokine profiles - e.g. aluminium salts (alum) -> form trapped particles (antigen) in depot -> slow antigen release -> Increase immune response + potent vaccine

25
Q

Vaccination programmes
Describe components of a successful vaccination programme?

A
  • Case findings (surveillance)
  • Movement control
  • Effective vaccine
26
Q

Why is it difficult to produce a HIV vaccine?

A
  • Increased mutation rate
  • Danger of reversion to virulence (stops use ALV to induce Tc cells)
  • Newer vaccine technology being used to develop
27
Q

Describe passive treatments for vaccines?

A
  • Maternal transfer, treatment with AB from another source - serum -> prophalyxis +/OR treatment -> Rapid short effect use
  • Used for rabies -> human rabies immunoglobin or equine rabies Ig (horse serum) use