56. Scientific Basis of Vaccines

Question 1

Vaccine

Answer 1

Material from an organism that will actively enhanced adaptive immunity.
Produces an immunologically “primed” state the allows for a rapid secondary immune response on exposure to antigen prevention of disease.

Long lasting requires immunological memory
Antibodies and/or T cells (humoral and cell mediated immunity)

Question 2

Vaccine rationale

Answer 2

• Protection of the individual ~ decrease rate/severity
• Protection of the population ~ Herd Immunity
• Can lead to the eradication of disease

Question 3

The vaccine Paradox

Answer 3

Herd Immunity – memory boosted by

• periodic outbreaks of disease in community
• vaccines

• As disease rates decline - no natural boosting -> Increases importance of vaccination take up rates

Question 4

Active vs passive immunity

Answer 4

ACTIVE IMMUNITY
•Innate, adaptive   (CMI; antibodies)
•Natural exposure (carriage)
•Infection 
•Vaccination ~ Long effect 

PASSIVE IMMUNITY
•(antibody from another source: serum)
•Prophylaxis and/or treatment
Short effect

Question 5

Immune responses to antigen

Answer 5

PRIMARY EXPOSURE
•5-7 days antibody response
•2 weeks for a full response
•IgM -> IgG switching
•memory B and T cells

SECONDARY RESPONSE
•2 days for full protective response
•(prior exposure)

• Post-exposure immunoprotection due to response vs specific antigens e.g. surface proteins, polysaccharides, toxins good targets for vaccine candidates

Question 6

Vaccines : general principles

Answer 6

1) Induce correct TYPE of response
- Antibodies -> Polio virus
cell mediated immunity tuberculosis

2) Induce response in RIGHT PLACE
- mucosal - sIgA -> ‘flu; polio
- systemic (blood stream) -> Yellow fever

3) Duration of protection
- short-term (travel) -> antibody sufficient
- long-term -> memory essential
• Boosters
- natural (seasonal epidemics; carriage)
- vaccines
•Type of infection
- long incubation time - systemic -> measles
- short incubation time – surface -> cholera

4. Age of vaccination
   - Maternal antibodies in neonate
   - sIgA in milk lasts for ~ 6 months
   - Problem for live attenuated vaccines e.g. MMR
   • Virus neutralised by maternal antibody -> no protection
   •Vaccinate > 9 months
   But… many babies infected by then in endemic areas.

Question 7

Types of Vaccines I

Answer 7

1) Live, attenuated organism
(e.g. BCG, MMR)
by:- serial passage,
low temperature adaptation,
recombinant genetics ( S.typhi Ty21a; galE + aroA/B/C mutant)
selection of natural attenuated strains

2) Killed, whole organism
e.g. pertussis, flu (old type)
polio (Salk type), cholera, HepA
reactogenicity
boosting required

3) Sub-unit vaccines (individual components)
- proteins
- toxoids (diphtheria; tetanus)
- peptides (synthetic)
- polysaccharide
- recombinant proteins
- sub-cellular fractions
- surface antigens
- virulence determinant

Question 8

Vaccine Adjuvants and Delivery Systems

Answer 8

• enhance immune response to antigen
• promote uptake and antigen presentation
• stimulate correct cytokine profiles