Here are some facts:
What makes a vaccine succesful?
- The disease is not asymptomatic
- No carriage
- No animal reservior
- Vaccine stability
- Large infectious dose of disease needed
There are three basic types of vaccine in use today:
Killed vaccines: These are preparations of the normal (wild type) infectious, pathogenic virus that has been rendered nonpathogenic, usually by chemical treatment such as with formalin that cross-links viral proteins.
Attenuated vaccines: These are live virus particles that grow in the vaccine recipient but do not cause disease because the vaccine virus has been altered (mutated) to a non-pathogenic form; for example, its tropism has been altered so that it no longer grows at a site that can cause disease.
Sub-unit vaccines: These are purified components of the virus, such as a surface antigen.
|VACCINES - GENERAL
Advantages of attenuated vaccines:
They activate all phases of immune system. They elicit humoral IgG and local IgA.
They raise immune response to all protective antigens. Inactivation, such as by formaldehyde in the case of the Salk vaccine,may alter antigenicity.
They offer more durable immunity and are more cross-reactive. Thus they stimulate antibodies against multiple epitope which are similar to those elicited by the wild type virus.
They cost less to produce.
They give quick immunity in majority of vaccinees.
In the cases of polio and adenovirus vaccines, administration is easy.
These vaccines are easily transported in the field.
They can lead to elimination of wild type virus from the community.
Disadvantages of Attenuated vaccine:
Mutation. This may lead to reversion to virulence (this is a major disadvantage).
Spread to contacts of vaccinee who have not consented to be vaccinated. (This could also be an advantage in communities where vaccination is not 100%). Spread of the vaccine virus that is not standardized and may be mutated.
Sometimes there is poor "take" in tropics.
Live viruses are a problem in immunodeficiency disease patients.
Advantages of inactivated vaccine:
- They give sufficient humoral immunity if boosters given.
- There is no mutation or reversion (This is a big advantage).
- They can be used with immuno-deficient patients.
- Sometimes they perform better in tropical areas.
Disadvantages of inactivated vaccines:
- Some vaccinees do not raise immunity.
- Boosters tend to be needed.
- There is little mucosal / local immunity (IgA).
- Higher cost.
- In the case of polio there is a shortage of monkeys.
- In the case of smallpox there have been failures in inactivation leading to immunization with virulent virus.
P.S. I bet this will come up (!)