7. Vaccines

Question 1

Immunisation

Answer 1

Artificial process by which an individual is rendered immune

Question 2

Passive immunisation

Answer 2

No active immune response in the recipient

Protection is temporary
-due to no memory cells

Question 3

Active immunisation

Answer 3

Aka vaccination

Recipient develops a protective adaptive immune response

Question 4

VZV in pregnancy

Answer 4

VZV during pregnancy can cause fetal complications

Exposure is treated immediately with vaccine

Indications for vaccine: VZV IgG negative or equivocal

Question 5

Components of a vaccine

Answer 5

Antigen

Adjuvants
- increase immunogenicity of the vaccine

Excipients
-Increases vaccine integrity (ie various dilutents and additives)

Question 6

Live-attenuated vaccines

Give examples

Answer 6

Live\weakened organisms

Organism are cultured to live in non-physiological conditions so that it is unable to cause disease

E.g measles, mumps, rubella, BCG

Question 7

Pros and cons of live vaccine

Answer 7

Repeated boosting not required

Intracellular response leads to good CD8 response

Replication occurs within host

Cons
-May revert to wild type

• Storage problems- may revert to wild type
• Immunocompromised pts may develop disease

Question 8

Inactivated vaccine

Answer 8

Entire organism used, but physical or chemical methods used to destroy viability (e.g. formaldehyde)

E.g. Influenza, Hep A

Question 9

Subunit vaccines

Answer 9

Uses only critical part of the organism

• Toxins are detoxified to become ‘toxoids’
  e. g Tetanus vaccine, Hep B, HPV

Question 10

General Principals of vaccination

Answer 10

Most generate a long lasting high IgG antibody response

Most effective are when natural exposure leads to protective immunity

Question 11

Varicella-Zoster Vaccine

Answer 11

Primary infection = chickenpox

Cellular and humoral immunity provide lifelong protection, but viruses establishes permanent infection of sensory ganglia

Viral reactivation=zoster

Particularly elderly, fairly debilitating and may cause long-term neuropathic pain

Question 12

VZV vaccine

Answer 12

Live attenuated
-Induces anti-VZV antibodies

95% effective at preventing chickenpox

3-5% post-vaccination varicella infection

Question 13

Zoster vaccination

Answer 13

• Similar to VZV vaccine, but higher dose

- Boosts memory T cell responses to VZV

Question 14

Poliomyelitis (polio)

Answer 14

• Enterovirus causes infection in oropharynx and GI tract (alimentary phase)
• Spreads to peyers patches then disseminated via lymphatics

Haematogenous spread

1% develop denervation and flaccid paralysis

Question 15

Tb infection

Answer 15

• During primary infection, MTB establishes infection within phago-lysosomes of macrophages.
• Macrophages present TB antigen to MTB-specific CD4 T cells, which secrete IFN-g – this activates macrophages to encase TB in granuloma.
• May be visible as a calcified lesion on plain CXR (Ghon focus)

Most TB thought to be re-activation of this primary infection

Question 16

Tb vaccination

Answer 16

BCG- intradermal injection

Aims to increase Th1 (IFN-g) cell responses to M bovis, conferring protection against MTB

80% effective in preventing disseminated TB/ TB meningitis in children; little or no effect on pulmonary TB

Question 17

Pros and cons of killed (inactivated) vaccines

Answer 17

No potential for reversion
Safe for immunocompromised
Stable in storage

Cons

• Mainly CD4/ antibody response
• Responses less durable then live vaccines
• Generally boosters required
• Higher uptake generally required to achieve herd immunity

Question 18

Influenza vaccine

Answer 18

Protective antibody responses largely directed against Haemagglutinin and Neuramidase (external antigen)

Difficulties: antigenic shift

Question 19

Tetanus vaccine

Answer 19

-Pre-formed high-affinity IgG antibodies can neutralise the
toxin molecules in the circulation; the immune complexes
are then removed via the spleen

-Anti-toxin can also be given in established cases (passive immunisation)

Question 20

Polysaccharide capsules

Answer 20

• Thick polysaccharide coats of Streptococcus pneumoniae and Neisseria meningitidis make them resistant to phagocytosis
• Vaccines for these organisms formed of purified polysaccharide coats
• Vaccines formed of purified polysaccharide coats; aim to induce IgG antibodies that improve opsonisation

Question 21

Vaccine conjugation

Answer 21

Naive B cell expressing surface IgM recognises polysaccharide antigen. Antigen is internalised together with the protein conjugate

Conjugate is processed in the class II pathway. Naive B cell presents peptides from the conjugate to a helper T cell with the correct receptor.

T cell helps the B cell to perform affinity maturation, but antibody is specific for the polysaccharide and not for the protein conjugate

Question 22

HPV subtypes commonly associated with cervical cancer

Answer 22

16 and 18

Question 23

Pros and cons of subunit vaccines

Answer 23

Extremely safe
Work well where primary infection may be prevented by an antibody response
Works when the virus cannot easily be cultured eg HPV and Hep B

Cons
Development requires detailed knowledge of virology, pathogenesis and immunology
Specialised and expensive production
Weaker immune responses – boosting often needed and response rate varies

Question 24

Examples of subunit vaccines

Answer 24

Hep B

HPV

Tetanus