Vaccines

Question 1

Who realised the connection between people who were in regular contact with cows infected with cowpox not themselves becoming infected with smallpox?
When was the last natural case of smallpox?
Who developed the first attenuated Rabies vaccine?

Answer 1

Edward Jenner in 1796.
1977.
Louis Pasteur in 1985

Question 2

What is a vaccine?

Answer 2

The name derives from Vacca (Latin for cow) due to Edward Jenners involvement. A Vaccine is a non-toxic antigenic preparation that are injected, inhaled or ingested. Induces a specific immune response against pathogen without the disease process.

Question 3

What would an ideal vaccine do?

Answer 3

It should prime the recipients immune system to generate immunological memory.
Should confer lifelong immunity with a single immunisation, have no side effects and be >95% effective.
Should be simple, inexpensive, easily transportable and stable in extreme heat/moisture.

Question 4

What are the reasons for vaccination?

Answer 4

Antimicrobials mostly used for treatment,
May be used for preventing infection and disease,
Antimicrobials are not always acceptable for prevention,
Vaccines prevent disease,
They are cost effective,
They are cheap,
They offer efficient protection

Question 5

What are the requirements of a good vaccine?

Answer 5

They must be safe, 
Effective, 
Cheap,
Easy to administer, 
Preferably oral, 
Defined composition, 
Known mode of attenuation in the case of live vaccines.

Question 6

What are the types of vaccine.

Answer 6

Killed attenuated (inactivated)- e.g. Formaldehyde treated.
Live attenuated- specific mutant.
Component/subunit- e.g. Surface protein.
Conjugate- poor antigen covalently linked with immunological carrier.
DNA- correct copy of single gene.

Question 7

Describe inactivated viruses.

Answer 7

They are most commonly used at present. They are whole culture or bacterial cells enriched with pathogenic determinants, or parts of bacterial cells.
They are inactivated with formaldehyde, and preserved with phenol. Attenuated vaccines are mixed with adjuvant.

Question 8

Describe the use of inactivated vaccines.

Answer 8

They are administered intramuscularly, generally with two or more injections. This vaccine elicits IgM and IgG antibodies. The vaccine provides poor immunity as local mucosal surfaces and the duration of immunity is poor. If the mother is vaccinated she will have provide passive immunity for her offspring.

Question 9

What are adjuvants?

Answer 9

Inactivated vaccines contain adjuvants that enhance the immune response to the vaccine. They induce inflammation at the site of the vaccination. Adjuvants can cause local irritation and swelling at the site of vaccination. Adjuvants used are aluminium hydroxide, aluminium phosphate, alum, mineral oil such as liquid paraffin.

Question 10

Inactivated vaccines contain preserved antigens, preserved through the presence of phenol. List these preserved antigens.

Answer 10

Fimbriae, 
Capsules, 
Outer membrane proteins, 
Cell wall lipopolysaccharides,
Iron binding proteins and heat shock proteins,
Prototoxins and toxins/toxoids, 
Other secreted antigens.

Question 11

How are live vaccines administered?

Answer 11

They are administered parenterally (any way that isn’t enterally, e.g. Intravenously) for systemic humoral and cellular immunity.
They can also be administered intranasally for the immunity in respiratory tract.
Can be administered enterally for intestinal and lactogenic immunity.

Question 12

What is one aim, benefit and disadvantage of using live vaccines?

Answer 12

The aim of them is to produce a modified organism that mimics the natural behaviour of the original organism but does not cause significant disease.
Replication of the organism provides a sustained dose of antigen and appropriate immune responses.
Possesses limited viability in the host’s environment.

Question 13

What are the advantages of using live attenuated bacterial vaccines?

Answer 13

Self limiting infection mimicking on a small scale the natural infection.
In theory will produce all antigens normally expressed in vivo by the pathogens.
May stimulate immune responses in ways which resemble those elicited during natural infection.
Can elicit mucosal immune responses if administered via the mucosa e.g. Orally.

Question 14

What are the potential disadvantages of using live vaccines?

Answer 14

There is the possibility of adventitious agents in the cells and medium.
There is the possibility that the vaccine will revert to wild type (become virulent),
They have a limited shelf life,
They require cold storage,
They provide a risk to immunocompromised individuals.

Question 15

Give an example of a successful live polio vaccine.

Answer 15

Oral live polio vaccine, gives better mucosal antibody responses than the killed vaccine.

Question 16

Describe component vaccines.

Answer 16

They contain one or more protective antigens. These can be toxoids, secreted antigens or component/structural proteins. These are becoming increasingly used.
For successful component vaccines, moderate amounts of antigens are required, and they are administered with adjuvant.

Question 17

What are purified antigen vaccines?

Answer 17

These are vaccines composed of molecules purified directly from the pathogen. For them to be made, the molecules that generate the immune response need to be identified. These can be polysaccharides, proteins or exotoxins.

Question 18

What are conjugate vaccines?

Answer 18

These rely on covalently linking a protein carrier to a polysaccharide. This converts them into T cell dependent antigens.
The protein carriers include: tetanus toxoid, diphtheria toxoid and outer membrane protein from meningococcus group B.
Has been successful with: haemophilus influenza.

Question 19

What are the problems with traditional technology when making bacterial (killed) vaccines?

Answer 19

The killed pathogen used may initiate an immune response with a poor efficacy that responds to an irrelevant antigen.

Question 20

What are the problems with traditional technology when making bacterial (subunit) vaccines?

Answer 20

The critical epitopes may be destroyed through inactivation. They can be poorly immunogenic and may still be toxic if insufficiently treated.

Question 21

What are the problems with traditional technology when making bacterial (live) vaccines.

Answer 21

They are produced by non-specific methods. The basis for attenuation is usually unknown. Control of this attenuation is difficult and they may revert to virulence in vivo.

Question 22

Describe the need for mucosal vaccines.

Answer 22

Mortality and morbidity of deaths from infectious diseases is high, with deaths from infectious disease in 2001 being 14 million.
Current vaccines are unaffordable in developing countries, have a poor efficacy and their need for cold storage makes them difficult to transport). Mucosal vaccines could elicit both mucosal and systemic immunity.

Question 23

Where are most infectious diseases acquired?

What are the defences at these sites?

Answer 23

At mucosal membranes.
Defences are the innate immunity of the anatomic barrier. Additionally the fact that there are mucosal associated lymphoid tissues at these sites such as Peyers patches. These secrete B cells and T cells.

Question 24

What is the surface area of Mucosal associated lymphoid tissue?

Answer 24

> 400m2

Question 25

Describe a study where the effect of mucosal targeted vaccines is more effective than other forms.

Answer 25

A study conducted on mice with the flu vaccine showed that intra nasal administration resulted in considerably higher IgA antibody production than subcutaneous administration.

Question 26

What are the benefits of mucosal immunisation?

Answer 26

There is a mucosal and systemic response,
There is no need to use needles,
It is less reactogenic.

Question 27

What are the problems with developing mucosal vaccines?

Answer 27

Most soluble or non-relocating agents are very poor mucosal immunogens. The reasons for this are that many antigens to make it to the sites of mucosal associated lymphoid tissues. This is due to entrapment, degradation and removal of antigens through the use of the hosts digestive system. Also vaccines given mucosally have low immunogenicity.

Question 28

List some approaches to developing mucosal vaccines.

Answer 28

Encapsulation,
Mucosal adjuvants,
Transgenic plants,
Live attenuated microbes,
Live vectors.

Question 29

Describe the Ty21a live oral typhoid vaccine.

Answer 29

N-methy-N-nitro-N-Nitrosoguanidine (NTG) mutagenesis of Salmonella Typhi Ty2 results in it being used as a live oral vaccine. It is extremely safe, the bacteria possessing multiple mutations. In absence of galactose, it makes rough LPS thus is avirulent. In the presence of galactose it makes smooth LPS but lyses due to accumulation of toxic compounds thus is still avirulent.

Question 30

Deletion mutations occur in which genes for Salmonella typhi for the oral live attenuated vaccine?
How many doses are required for the vaccine to be effective?

Answer 30

In galE and via.

Multiple doses.

Question 31

Development of a new vaccine depends upon?

Answer 31

Protective antigens with intact epitopes,
The requirements for the induction of immunity,
Knowledge of the biology of the infectious agent and the existence of model systems,
Possibly side effects,
Economic factors,
Compliance and implementation.

Question 32

Outline the modern approach to constructing live vaccines.

Answer 32

Identify target genes,
Construct mutant,
Inactivate at least 2 genes,
Test if attenuated in animal model.

Question 33

What are multi-talent vaccines?

Answer 33

This is a strategy which would employ the use of Salmonella to protect against tetanus.

Question 34

What are the advantages of using love bacteria as carriers of foreign antigens?

Answer 34

It would improve the immunogenicity of the vaccine,
It would stimulate all arms of the immune system,
There is no need for injection for immunisation,
Antigens from unculturable organisms could be expressed,
Multivalent vaccines.

Question 35

What are the advantages of using salmonella as a vector?

Answer 35

Salmonella stimulates all arms of the immune system.
Salmonella reside in antigen presenting cells,
The vaccine can be orally administered,
The genetics are advanced,
Antigens can be expressed from organisms that are hard to culture.

Question 36

How many deaths does tetanus cause in the developing world?
What is the current tetanus vaccine?
What are the problems with this vaccine?

Answer 36

Tetanus causes 1 million deaths per year in the developing world.
The current vaccine is a formaldehyde treated tetanus toxin.
The problems with the vaccine are that several doses are needed for complete immunity and that it needs to be administered parenterally.

Question 37

What would be used to genetically transform salmonella to result in it providing resistance to tetanus?

Answer 37

Transform with the FrgC gene which expresses a non-toxic fragment of the tetanus toxin. This is transformed into the plasmid along with the promoter and the AmpR gene for resistance to select for the bacteria.

Question 38

Who published the fraudulent paper in the Lancet on vaccines causing autism?
This led to immunisation rates dropping from what to what?
How many children in the US were no immunised because of this study.

Answer 38

Andrew Wakefield.
92% to 73%
125000 children not immunised.