Vaccines

Question 1

Explain how vaccines elicit an immune response and provide protection from disease

Answer 1

Vaccines contain antigens that stimulate immune response and results in immunologic memory (production of memory T & B cells)
Subsequent exposure to the same antigen will result in faster and stronger secondary immune response

Question 2

List the different types of vaccines

Answer 2

1) Live vaccines
2) Inactivated vaccines
3) Subunit vaccines
4) Toxoid vaccines
5) Recombinant vaccines

Question 3

Live vaccines

1) Characteristics
2) Advantages
3) Limitations
4) Examples

Answer 3

1) Characteristics
- Contains weakened (attenuated) virus
- Often weakened by passing repeatedly through tissue culture in which it replicates poorly

2) Advantages
- Highly immunogenic (activates killer T cells) –> 1-2 doses can provide lifelong immunity

3) Limitations
- Sensitive to temperature changes –> must be refrigerated
- Less safe for patients with weakened immune system –> concerns over uncontrolled replication of resulting in disease

4) Examples
- Measles, mumps, rubella, rotavirus, varicella

Question 4

Live vaccines should be avoided in

Answer 4

1) Pregnant women
2) Young infants
3) Severely immunocompromised patients
4) Administering together with other live vaccines / antibody containing products
- Live vaccines should be given at least 28 days apart
- Live vaccines should be given 3-10 months apart from antibody-containing products

Question 5

Inactivated vaccines

1) Characteristics
2) Advantages
3) Limitations
4) Examples

Answer 5

1) Characteristics
- “Whole, killed” vaccine
- Killed via heat/chemical treatment

2) Advantages
- Easy to store & transport
- Low risk of causing infections

3) Limitations
- Stimulates weaker immune response –> may require several doses & boosters

4) Examples
- Polio, hepatitis A, rabies

Question 6

Subunit vaccines

1) Characteristics
2) Advantages
3) Limitations
4) Examples

Answer 6

1) Characteristics
- One or more parts of virus (e.g. protein / polysaccharide / conjugate) are isolated and used to evoke immune response

2) Advantages
- Low risk of adverse events
- Can be used in patients with weakened immune system

3) Limitations
- May require boosters
- Difficult to manufacture

4) Examples
- Influenza, hepatitis B, pertussis, Pneumococcus

Question 7

Toxoid vaccine

1) Characteristics
2) Advantages
3) Limitations
4) Examples

Answer 7

1) Characteristics
- Toxin produced by pathogen is deactivated & used to stimulate immune response

2) Advantages
- Doesn’t spread and cause disease
- Stable –> easy to distribute

3) Limitations
- May require boosters

4) Examples
- Diphtheria, tetanus

Question 8

Recombinant vaccines

1) Characteristics
4) Examples

Answer 8

1) Characteristics
- Manufactured by genetic engineering
- May contain no actual virus OR contains a modified strain of the virus

4) Examples
- Hepatitis B, HPV

Question 9

Common routes of transmission

Answer 9

1) Respiratory (airborne, droplets)
2) Food & water
3) Vector-borne
4) Blood and body fluids (sexual, mother-to-child)
5) Contact (bites, cuts)

Question 10

List vaccines available in preventing common infections transmitted by different routes

1) Respiratory (airborne, droplets)
2) Food & water
3) Vector-borne
4) Blood and body fluids (sexual, mother-to-child)
5) Contact (bites, cuts)

Answer 10

1) Influenza, Pneumococcus, H. influenzae, diphtheria, pertussis, meningococci, chickenpox, measles, mumps, rubella, BCG (tuberculosis)
2) Hepatitis A, typhoid, cholera, rotavirus
3) Yellow fever, Japanese encephalitis, dengue (concerns over safety & efficacy), malaria (in development)
4) Hepatitis B, HPV
5) Tetanus, rabies, shingles

Question 11

Describe principles of herd immunity

Answer 11

Herd immunity occurs when a large enough proportion of the population is vaccinated –> prevents spread of disease
Most community members are protected, including unimmunized individuals
High vaccination rates protect the most vulnerable (people who cannot be vaccinated) via herd immunity
Level of vaccination needed to achieve herd immunity depends on how contagious disease is

Question 12

List the vaccines in Singapore’s childhood immunization schedule

Answer 12

1) BCG (tuberculosis)
2) Diphtheria, tetanus, acellular pertussis (DTaP)
3) H. influenzae type B
4) Pneumococcal disease
- Pneumococcal conjugate (PCV10 / PCV13)
- Pneumococcal polysaccharide (PPSV23)
5) Hepatitis B
6) Varicella
7) Influenza
8) Inactivated poliovirus
9) Measles, mumps, rubella (MMR)
10) HPV (HPV2 / HPV4)

Question 13

List the vaccines in Singapore’s adult immunization schedule

Answer 13

1) Influenza
2) Pneumococcal conjugate (PCV13)
3) Pneumococcal polysaccharide (PPSV23)
4) Tetanus, reduced diphtheria & acellular pertussis (Tdap)
5) Hepatitis B
6) HPV (HPV2 / HPV4)
7) Varicella
8) Measles, mumps, rubella (MMR)

Question 14

General considerations in vaccine use

Answer 14

1) Effectiveness
2) Adverse effects
3) Contraindications / Precautions
4) Simultaneous administration
5) Missed doses

Question 15

Factors affecting effectiveness of vaccines

Answer 15

1) Administration
- Site of administration / Proper administration
2) Patient age & immune status
- E.g. Influenza is less effective in 80 year old VS 60 year old
3) Cold chain problems
- Proper storage & distribution, at recommended temperatures, is important
- Especially for live vaccines (sensitive to temperature changes)

Question 16

Adverse effects of vaccines

1) Mild, common
2) Uncommon
3) Severe, rare

Answer 16

1) Pain at injection site, myalgia, headache
2) Fever, hematoma
3) Anaphylaxis, hypersensitivity

Question 17

Contraindications & Precautions of vaccines

Answer 17

1) Allergy to vaccine or components
2) Moderate-severe illness (fever > 38 degC)
3) Bleeding risk (on anti-coagulation or low platelet count) - Caution
4) Pregnancy (live vaccine)
5) Immunocompromised (live vaccine)

Question 18

Simultaneous administration of vaccines

1) Inactivated, non-living vaccines
2) Live vaccines

Answer 18

1) Inactivated, non-living vaccines
- Most can be administered simultaneously / within same day, without reducing efficacy/increase adverse effects
- Exception: PCV & meningococcal conjugate vaccine in patients with functional / anatomical asplenia - 4 week interval

2) Live vaccines
- Must be spaced at least 28 days apart

Question 19

Missed vaccine dose

Answer 19

Dose should be given as soon as possible

Additional dose generally not required

Question 20

Components in vaccine

Answer 20

1) Active components (antigens)
2) Adjuvants
3) Antibiotics
4) Stabilizers
5) Preservatives
6) Trace components

Question 21

Production of active components (antigens) in vaccines

Answer 21

Derived from virus/bacteria/toxin that causes the disease
Antigen is modified from its original form such that it is unable to cause disease but is still able to elicit immune response

Modification methods:

1) Treat with specific chemicals –> prevent replication
2) Treated such that it no longer causes disease
3) Isolate & use parts of disease-causing agent that do not cause serious symptoms

Question 22

Adjuvants

1) Function
2) How it works
3) Adverse effects
4) Examples

Answer 22

1) Function
- Enhance body’s immune response to the vaccine

2) How it works
- Thought to keep antigens at site of injection –> easily accessed by immune system

3) Adverse effects
- No evidence of serious adverse effects
- Might cause minor reactions near injection site

4) Examples
- Aluminium hydroxide
- Aluminium phosphate

Question 23

Components in vaccines - Antibiotics

1) Function
2) Examples

Answer 23

1) Function
- Used during manufacturing to prevent bacterial contamination
- Removed after manufacturing –> only residual amounts left in vaccine

2) Examples
- Gentamicin, Neomycin

Question 24

Components of vaccines - Stabilizers

1) Function
2) Examples

Answer 24

1) Function
- Ensures various components remain stable & effective –> enables vaccine to be storable

2) Examples
- Inorganic salts e.g. magnesium sulfate, magnesium chloride
- Mixtures of lactose, sorbitol, gelatin
- Monosodium glutamate, glycine

Question 25

Preservatives

1) Function
2) Examples

Answer 25

1) Function
- Prevent contamination of vaccine (especially in multi-dose vaccines)

2) Examples
- Thiomersal
- Phenol
- Phenoxyethanol

Question 26

Trace components

1) What are trace components
2) Examples

Answer 26

1) What are trace components
- Leftover from manufacturing process
- Components removed after manufacturing but residual amounts may still remain

2) Examples
- Formaldehyde –> detoxify bacteria & deactivate virus (amount remaining is several hundred times lower than smallest amount known to cause harm in humans)