Principles of Vaccines

Question 1

Why do we vaccinate?

Answer 1

Preventation of infectious disease in an individual/herd where the disease has health and welfare implications such as persistent infections

Question 2

Why do we vaccinate in production animals?

Answer 2

Improvement of economic benefits - so endemic infections are unable to occur

Question 3

How do vaccines work simply?

Answer 3

Expose the vaccinated animal to foreign antigens that cannot cause disease within the host - educating the immune system

Question 4

What is herd immunity?

Answer 4

The more people vaccinated against the pathogen the less liekly it is to spread (75 - 95% target rate of vaccination)

Question 5

What type of lymphocyte is responsible for response to secondary infection by a pathogen they are vaccinated against?

Answer 5

In the short and medium term antibody specifc to the antigen persists but for secondary infection memory lymphocytes with specificity for that antigen will persist for years and can mediate a response if secondary exposure occurs

Question 6

What are the ideal characteristics of a vaccine?

Answer 6

• Cheap to produce
• Consistency between batches
• Stable/long shelf life
• Easy administration
• Rapid/long lasting immunity in a single dose
• No adverse effects
• Clear benefit to all stakeholders

Question 7

What are Passive Immunisation vs Active Immunisation vaccines?

Answer 7

Passive Immunisation vaccines = injected with antibodies such as antiserum or also could mean colostrum a natural passive immunisation process
Active Immunisation = injected with foreign antigen i.e. toxoids, modified-live organisms, killed organisms, subunit antigens, recombinant DNA/RNA

Question 8

Why is vaccination of maternal animals important? give an example of a maternal vaccine given before parturition

Answer 8

Vaccinate the mother - the mother then passes the antibodies to her young via colostrum
e.g. Lactovac - contain multiple antigen. Vaccinate 3-12 weeks before calving, calf will drink colostrum which will include these antibodies

Question 9

What is Antiserum? give an example

Answer 9

A passive immunisatation where serum from a immunised animal is injected into an animal with no immunisation e.g. Tetanus antitoxin - antibodies from immunised horse injected into non-protected aniamls for immediate effect

Question 10

What is the purpose of passive immunisation ?

Answer 10

Used for short term protection - when an animal hasn’t been immunised against something such as tetanus

Question 11

What are the disadvantages and advantages to active immunisation?

Answer 11

It could take multiple doses of the vaccine to achieve immunity however, when immunity is achieved it usually is long lasting

Question 12

What are Toxoid vaccines?

Answer 12

A vaccine protective against bacteria that produce exotoxins to produce a pathogenic effect and example of this is tetanus - neutralising antibodies are effective at preventing harmful effects of toxins in the body

Question 13

How does tetanus affect a host?

Answer 13

Blocks release of inhibitory neurotransmitters (Glycine, GABA) and leads to spastic paralysis

Question 14

How does the tetanus toxoid vaccine work?

Answer 14

Toxoid = inactive form of bacterial toxin (modified for use in vaccines)
The tetanus toxoid is administered to horses stimulationg IgG production neutralising C.tetani

Question 15

What is a Killed (inactivated) vaccine?

Answer 15

A vaccine containing a dead/inactivated organism that can no loger cuase pathogenic effects but still contains antigen and can still initiate immune responses

Question 16

How do we kill virulent organisms for killed (inactivated) vaccines?

Answer 16

• Chemicals: Formaldehyde - crosslink proteins or Alkylating agents - crosslinks nucleic acids
• Heat or Radiation sterilising the organism

Question 17

What is a modified live (attenuated) vaccine?

Answer 17

A vaccine that has a modifed virulent organism that has reduced virulent (attenuated) effect, organism is still alive but grows so slowly it doenst cause disease - low virulence mutant organisms are selected (selective selection)

Question 18

How do we attenuate a virus in laboratories for vaccines?

Answer 18

Grow the virus in unusual conditions, virus mutates to suit those conditions (natural selection) and drives low virulence mutants
or
Genetic modification - targeted disruption of virulence genes

Question 19

What is a subunit vaccine?

Answer 19

A vaccine that contains purified subunits of pathogens that are needed to ellicit an immune response in the host

Question 20

What is a recombinant vaccine?

Answer 20

A vaccine containing a pathogenic gene antigen that is injected into the host and produces a recombinant protein in vivo and stimulates an immune response

Question 21

How do we produce recombinant vaccines?

Answer 21

1. Identify the gene encoding antigen
2. Clone this sequence into a Virus Vector or Plasmid DNA or as Naked DNA/RNA (mRNA)

Question 22

What is a mRNA vaccine (how do they work?) and give an example

Answer 22

A vaccine containing mRNA that encodes for a viral spike protein - mRNA enters human cells, spike protein is created and presented on cell surface, antibodies recognise spike protein and produce immune resposne, memory lymphocytes produced for future infection

Question 23

What are adjuvants and why are they added to vaccines?

Answer 23

Oily substances acting as a depot for antigen allowing a longer exposure of antigen to the immune system

Question 24

What are the quantitative and qualitative effects of adjuvants?

Answer 24

Quantitative - Added in killed and subunit vaccines to boost immunogenicity and increase antibody response
Qualitative - Alter antibody isotype produce or alter Th2:Th1 balance influencing cell-mediated vs antibody-mediated response