Defence and vaccination against infection H&S

Question 1

Active vs passive immunisation

Answer 1

Active immunisation

• Requires active induction of a host immune response, involving B cells and T cells
• Induction of a state of immunological readiness such that a first infection with a given pathogen is recognised as though it were a second infection by the same pathogen

Passive immunisation
- Transfer preformed immunological mediators (usually antibodies) into a normal individual to generate a state of enhanced immunity

• Both forms of immunisation may completely protect from infection, limit infection, or limit disease (e.g. anti-toxins)

Question 2

What does passive vaccination involve?

Answer 2

• Transfer of specific antibodies (gamma globulins):
  1. Tetanus
  2. Gangrene
  3. Snake bite
  4. Hep B
  5. Rabies
• Transfer of normal serum gammaglobulins
  Hypogammaglobulinaemia
• Maternal antibodies
  Placental IgG
  Colostral IgA

Question 3

How do adjuvants enhance immunogenicity?

Answer 3

• Induce inflammation
• Provide microbial signals to boost innate immunity
• Provide a long-lasting depot of antigen
• FEW ADJUVANTS ARE LICENSED FOR USE IN MAN

Question 4

Why could smallpox be eradicated by vaccination?

Answer 4

1. No subclinical infections: case detection is difficult when people are asymptomatic
2. Only one dominant variant
3. Vaccine was highly effective at inducing sterile immunity
4. No animal reservoir
5. Vaccination was coupled with active surveillance and containment

Question 5

Route of infection for Poliomyelitis. Where does it infect and what are the consequences of this?

Answer 5

• Oral route
• Infects gut, then invades blood
• Targets nerve cells and destroys them, leading to paralysis of infected tissues

Question 6

What makes poliomyelitis eligible for eradication?

Answer 6

• No long term asymptomatic carriers for poliovirus in immunocompetent individuals
• No non-primate reservoir in nature

Question 7

Inactivated vs attenuated polio vaccines (ADV vs DISADV)

Answer 7

Advantages of inactivated (dead) vaccine:

1. Effective
2. Can be incorporated into routine immunisation with DPT
3. Good stability in transport and storage
4. No risk for poliomyelitis in recipients and contacts
5. Safe for immunodeficient individuals

Disadvantages of the inactivated vaccine:

1. Does not induce gut immunity
2. Booster vaccines required
3. Administration as injection
4. Higher community vaccination levels required

Advantages of attenuated (live) vaccine:

1. Effective
2. Lifelong immunity
3. Induces immune response similar to natural infection
4. Indirect community immunisation through spread of attenuated virus
5. Administration is oral
6. Booster vaccines not required

Disadvantages of live vaccine:

1. Vaccine-induced (iatrogenic) poliomyelitis
2. Spread to contacts without consent
3. Unsafe for immunodeficient individuals

Question 8

Different types of vaccines? Examples of each

Answer 8

1. Live / attenuated
   - MMR
   - Varicella
   - Influenza (spray)
   - Rota virus
   - Yellow fever
2. Inactivated / killed
   - Polio
   - Influenza (injection)
   - Cholera
   - Hep A
3. Toxoid (inactivated toxin)
   - Tetanus
   - Diphtheria
4. Subunit / conjugate
   - Hep B
   - HPV
   - HiB
   - Pertussis
   - Pneumococcal
   - Meningococcal