Vaccines & Immunisation

Question 1

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

Answer 1

Immunological memory development from adaptive immunity is the basis of vaccination.

• 1st exposure to antigen leads to the development of primary immune response with the proliferation of activated B & T cells into effector cells to elicit host immune response
• Some effector B & T cells will be converted into memory B & T cells for a quicker heightened state of reactivity w/ shorter lag time against subsequent antigen exposures.
• As vaccines contain antigens to stimulate an immune response, such active immunisation will result in the development of immunological memory before actual exposure to pathogen.

Question 2

Briefly describe how live, attenuated vaccines are prepared.

Answer 2

Virus is weakened by repeatedly passing through tissue culture in which it replicates poorly.

Question 3

Briefly describe how inactivated vaccines are prepared.

Answer 3

Pathogens are treated with heat or chemicals to kill them before inoculation into the body.

Question 4

Briefly describe how subunit vaccines are prepared.

Answer 4

One or more parts of pathogens (e.g. proteins, polysaccharides or conjugates) are isolated and used to evoke an immune response.

Question 5

Briefly describe how toxoid vaccines are prepared.

Answer 5

Toxins produced by pathogens, instead of the pathogen itself, are deactivated & used to evoke an immune response.

Question 6

Briefly describe how recombinant vaccines are prepared.

Answer 6

Produced by genetic engineering; may not contain any actual viruses or may contain a modified strain of virus.

Question 7

Briefly describe the advantages & disadvantages of using live, attenuated vaccines for vaccination.

Answer 7

(+) More immunogenic & thus able to evoke immune response from killer T cells
(+) One or two doses can provide lifelong immunity
(-) Must be refrigerated (i.e. cold chain maintenance) to minimise risk of re-activation / proliferation
(-) Less safe for individuals with weakened immune systems

Question 8

What are the precautions considered before administering live, attenuated vaccines to patients?

Answer 8

1) Avoid in pregnant women (NOT due to congenital side effects)
2) Generally not given in infancy (due to circulating Ab from mother that can interfere w/ replication process of live vaccines)
3) Avoid in severely immunocompromised patients
- Hematologic or solid organ malignancies
- Immunosuppressive medications & chemotherapy
- HIV w/ CD4 < 200
4) Avoid giving another live vaccine w/in 28 days of first administration (prevent circulating Ab from previous vaccines from interfering w/ replication process)
5) Space 3-10 months apart from administration of Ab containing products (i.e. Ig or blood transfusion)

Question 9

Name a few examples of diseases in which live, attenuated vaccines are used.

Answer 9

1) MMR (measles, mumps & rubella)
2) Varicella (chickenpox & shingles)
3) Rotavirus

Question 10

Name a few examples of diseases in which inactivated vaccines are used.

Answer 10

1) Hepatitis A
2) Polio
3) Rabies

Question 11

Name a few examples of diseases in which subunit vaccines are used.

Answer 11

1) Hepatitis B
2) Influenza
3) Pertussis
4) Pneumococcal

Question 12

Name a few examples of diseases in which toxoid vaccines are used.

Answer 12

Diphtheria & tetanus

Question 13

Name a few examples of diseases in which recombinant vaccines are used.

Answer 13

1) Hepatitis B

2) HPV (human papilloma virus)

Question 14

Briefly describe the advantages & disadvantages of using inactivated vaccines for vaccination.

Answer 14

(+) Easy to store & transport, but maintenance of cold chain is still important
(+) Less immunogenic; thus can be used in patients w/ weakened immune systems
(-) Less immunogenic; thus elicit weaker immune responses
(-) Requires multiple doses & boosters to attain adequate immune response for protection

Question 15

Briefly describe the advantages & disadvantages of using subunit vaccines for vaccination.

Answer 15

(+) Easy to store & transport, but maintenance of cold chain is still important
(+) Less immunogenic; thus can be used in patients w/ weakened immune systems
(+) Low risk of ADR
(-) Less immunogenic; thus elicit weaker immune responses
(-) Can be difficult to manufacture
(-) Requires multiple doses & boosters to attain adequate immune response for protection

Question 16

Briefly describe the advantages & disadvantages of using toxoid vaccines for vaccination.

Answer 16

(+) Easy to store & transport, but maintenance of cold chain is still important
(+) Unable to cause disease or spread
(+) Stable & easy to distribute w/in host
(-) Less immunogenic; thus elicit weaker immune responses
(-) Requires multiple doses & boosters to attain adequate immune response for protection

Question 17

List the vaccines available in preventing common infections transmitted airborne or via droplets.

Answer 17

• Influenza
• Pneumococcus
• Meningococcus
• Diphtheria
• Pertussis
• Haemophila influenzae
• MMR (measles, mumps & rubella)
• Chickenpox
• BCG (Bacillus Calmette-Guerin) (for tuberculosis)

Question 18

List the vaccines available in preventing common infections transmitted via fluid or water.

Answer 18

Hepatitis A, typhoid, cholera & rotavirus

Question 19

List the vaccines available in preventing common infections transmitted vector-borne.

Answer 19

Yellow fever, Japanese encephalitis, dengue & malaria (in development)

Question 20

List the vaccines available in preventing common infections transmitted blood & body fluids.

Answer 20

Hepatitis B & human papilloma virus (HPV)

Question 21

List the vaccines available in preventing common infections transmitted via contact (bites/cuts).

Answer 21

Tetanus, rabies & shingles

Question 22

Describe the principles of herd immunity.

Answer 22

1) In a community with no one immunised, when an outbreak occurs, it will spread throughout the community easily.
2) In a community with some immunised, when an outbreak occurs, there is insufficient immunity as a community to prevent the spread of the outbreak.
3) In a community with a sufficient percentage of immunised individuals, most community members can be protected against the spread of the outbreak including unimmunised individuals.
4) Thus, the degree of herd immunity necessary is largely dependent on how contagious the virus is.

Question 23

List the vaccines included in Singapore’s childhood immunisation schedule.

Answer 23

• Bacillus Calmette-Guerin (BCG) for TB
• Hepatitis B
• DTap & Tdap (Diphtheria, tetanus & acellular pertussis)
• Inactivated poliovirus (IPV)
• Haemophilus influenzae type b (Hib)
• Pneumococcal conjugate (PCV10 or PCV13)
• Pneumococcal polysaccharide (PPSV23) (for specific indication / medical condition)
• Measles, mumps & rubella (MMR)
• Varicella (VAR)
• Human papilloma virus (HPV2 or HPV4) for females
• Influenza (INF)

Question 24

List the vaccines included in Singapore’s adult immunisation schedule.

Answer 24

• Hepatitis B
• Tdap (Tetanus, reduced diphtheria & acellular pertussis)
• Pneumococcal conjugate (PCV13)
• Pneumococcal polysaccharide (PPSV23) (for specific indication / medical condition)
• Measles, mumps & rubella (MMR)
• Varicella (VAR)
• Human papilloma virus (HPV2 or HPV4) for females
• Influenza (INF)

Question 25

What are some factors for consideration in ensuring the effectiveness of vaccines?

Answer 25

• Site of administration
• Patient’s age & immune status
• Cold chain problems

Question 26

What are some adverse effects observed as a result of vaccinations?

Answer 26

Mild & common: pain at injection site, headache & myalagia
Uncommon: fever & hematoma
Severe but rare: anaphylaxis & hypersensitivity reactions

Question 27

What are the contraindications & precautions taken when administering vaccines?

Answer 27

C/I: Pregnancy & severely immunocompromised patients (for live, attenuated vaccines); allergic reactions to vaccines or components
Precaution: Bleeding risk (on anticoagulants or low platelet counts) & moderate / severe fever (> 38 degC)

Question 28

Is simultaneous administration of vaccines possible?

Is there any exception to this?

Answer 28

Yes, most vaccines can be administered w/in the same day w/o reduction in efficacy or increasing ADR.

One exception is PCV & meningococcal conjugate vaccine in pt. w/ functional or anatomical asplenia; 4-week interval is needed between the two vaccines to avoid interference.
Another exception is to avoid giving another live vaccine w/in 28 days of first administration.

Question 29

Explain the purpose of adding adjuvants in the formulation of vaccines.

Answer 29

Enhance immune response, esp. in inactivated, subunit & toxoid vaccines.

• Thought to keep antigens near site of injection
• No evidence of serious ADR, but may cause minor reactions near injection site

Question 30

Explain why antibiotics may be found in the formulation of vaccines.

Answer 30

Leftover / Residue from production of vaccines to reduce bacterial contamination.

Question 31

Explain why stabilisers are added to the formulation of vaccines.
Name some examples of stabilisers used in this case.

Answer 31

Ensure various components in the vaccines remain stable & effective under storage.
- Mg salts or mixtures of lactose, sorbitol & gelatin are used as stabilisers.

Question 32

Explain why preservatives are added to the formulation of vaccines.

Answer 32

To prevent contamination in vaccines.

Question 33

Explain why trace components may be found in the formulation of vaccines.

Answer 33

Leftover / Residue from production of vaccines to deactivate viruses & detoxify bacteria (e.g. formaldehyde), but amount remaining is several times lower than min. amount to cause harm.