Vaccines

Question 1

Define

Passive immunity

Answer 1

Immunity developed without the individual’s own cells, whether natural (e.g. maternal antibodies crossing the placenta or in the colostrum/breast milk) or artificial (inoculation with monoclonal antibodies, use of convalescent plasma)

Question 2

What are the types of vaccines?

Answer 2

• Live attenuated vaccines
• Non-live vaccines, including whole pathogen and subunit vaccines
• Reassortant live vaccines
• Vector and nucleic acid-based vaccines

Question 3

How are pathogens usually attenuated for use in a live vaccine?

Answer 3

A series of in vitro cell cultures (e.g. in chick embryo cells), which makes the pathogen better at infecting and replicating in the culture but less adapted to the original human host

Question 4

What are the advantages and disadvantages of live attenuated vaccines?

Answer 4

Advantages

• Provide robust immunity to the whole spectrum of antigens the pathogen possesses
• Immunity is more long-term, after only one or two doses

Disadvantages

• Clinical disease can occur, although usually milder
• Unsuitable for immunocompromised individuals

Question 5

What type of pathogen is most suitable for live attenuated vaccines?
| (virus, bacteria, protozoa, etc.)

Answer 5

Viruses, as they contain fewer genes and attenuation is easier and more reliable

Question 6

What are examples of viral live attenuated vaccines?

Answer 6

• Measles
• Mumps
• Rubella (often combined as MMR)
• Varicella (often combined as MMRV)
• Oral polio vaccine (OPV)

Question 7

What are examples of bacterial live attenuated vaccines?

Answer 7

Bacillus Calmette–Guérin (BCG) vaccine for tuberculosis, which is the only bacterial live attenuated vaccine currently in use

Question 8

What are the advantages and disadvantages of the live OPV vaccine over the inactivated IPV vaccine?

Answer 8

• OPV is more easily administered as it is formulated as oral drops, not an IM injection
• OPV may be better at inducing mucosal immunity than IM vaccines
• OPV can mutate into a virulent form and cause poliomyelitis. For this reason OPV is usually discontinued in favor of IPV after endemic polio is contained

Question 9

What are non-live vaccines?

Answer 9

Vaccines that do not contain any living or infectious particles, so they cannot cause disease

• For bacteria, they are called killed vaccines
• For viruses, they are called inactivated vaccines, as viruses were not alive to begin with

Question 10

What are the advantages and disadvantages of non-live vaccines?

Answer 10

Advantages

• Safer than live attenuated vaccines
• Safe for use in immunocompromised patients

Disadvantages

• Less immunogenic than live vaccines
• Shorter duration of protection, requiring several booster shots

Question 11

What are the types of non-live vaccines?

Answer 11

• Whole pathogen vaccines
• Subunit vaccines, including
  
  • toxoid vaccines
  • polysaccharide and conjugated vaccines

Question 12

How are viruses and bacteria inactivated for non-live vaccines?

Answer 12

• Heat
• Radiation
• Chemicals such as formalin/formaldehyde

Question 13

What are examples of whole pathogen non-live vaccines?

Answer 13

• Inactivated polio vaccine (IPV)
• Whole-cell pertussis
• Rabies
• Hepatitis A

Question 14

What are the kinds of fragments selected for subunit vaccines?

Answer 14

• Proteins
• Polysaccharides
• Parts of a virus that may form virus-like particles (VLPs)

Question 15

What are examples of subunit vaccines (that are neither toxoid nor polysaccharide)?

Answer 15

• Inactivated split and subunit seasonal influenza
• Acellular pertussis

Question 16

How are subunits prepared for use in vaccines?

Answer 16

• Purification from the whole pathogen, e.g. acellular pertussis
• Recombinant genetic engineering, e.g. hepatitis B surface antigen (HBsAg), the first malaria vaccine

Question 17

Cells of what organism are used for preparation of subunit vaccines by recombinant genetic engineering?

Answer 17

Yeast (S. cerevisiae), as it has a eukaryotic protein translation system, allowing for posttranslational modifications

Question 18

How does acellular pertussis vaccine compare to whole-cell pertussis vaccine?

Answer 18

Acellular pertussis is less immunogenic, as it contains 1–5 highly purified antigens, compared to 3000 in whole-cell pertussis

Question 19

What are examples of toxoid vaccines?

Answer 19

The toxins of

• Diphtheria (Corynebacterium diphtheriae)
• Tetanus (Clostridium tetani)

Question 20

How are toxins prepared for toxoid vaccines?

Answer 20

Inactivation by using heat, chemicals (e.g. formaldehyde), or both

Question 21

What are the advantages and disadvantages of toxoid vaccines?

Answer 21

Advantages

• Provide immunity to the toxins, which are sometimes more virulent than the pathogen itself

Disadvantages

• Do not prevent replication of the pathogen upon infection
• Do not reduce the risk of transmission; no herd immunity is formed

Question 22

What are examples of polysaccharide vaccines?

Answer 22

• Pneumococcus conjugate vaccine
• Haemophilus influenzae type B

Question 23

How is the short-term immunity of polysaccharide vaccines improved?

Answer 23

Conjugation to an immunogenic protein, which transforms the immune response to a T cell-dependent response

Question 24

What is a reassortant live vaccine?

Answer 24

A vaccine where the capsid of the target virus is combined with the genome of a known, less virulent vector virus (e.g. a bovine virus that has poor virulence in humans)

Question 25

What is an example of a reassortant live vaccine?

Answer 25

Reassortant rotavirus vaccine

Question 26

Define

Adjuvant

Answer 26

A substance that can enhance and modulate the immunogenicity of an antigen used in a vaccine

Question 27

In what type of vaccine are adjuvants usually not required?

Answer 27

Live attenuated vaccines, as these vaccines actively replicate and self-enhance in the body

Question 28

What is the most common adjuvant in use?

Answer 28

Aluminum salts (alum)

Question 29

What are the current problems facing vaccination efforts?

Answer 29

• Pathogens with multiple serotypes (e.g. dengue, S. pneumoniae)
• Pathogens with wide antigenic hypervariability (e.g. HIV)
• Pathogens with an intracellular phase that is predominantly controlled by T-cell responses, not by antibodies (e.g. tuberculosis, malaria)

Question 30

What are the vaccines on the national vaccination schedule in Jordan?

Answer 30

• BCG
• IPV
• OPV
• DPT
• DPT, IPV, Hib (H. influenzae type B)
• HBV
• MMR

Question 31

Define

Active immunity

Answer 31

Immunity formed using the individual’s own cells, whether natural (by infection with the pathogen) or artificial (by vaccination)