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 TABLE 1 Common currently used anti-viral vaccines Virus Vaccine Type Micrograph Links Polio (Salk) Inactivated Transmission electron micrograph of poliovirus type 1. CDC/Dr. Joseph J. Esposito jje1@cdc.gov CDC, MMWR (requires Acrobat) Polio (Sabin) Attenuated Notice to Readers: Recommendations of the Advisory Committee on Immunization Practices: Revised Recommendations for Routine Poliomyelitis Vaccination Rabies Original rabies vaccine developed by Pasteur. It was the first attenuated viral vaccine. Passed through nerve cords of rabbits. Current vaccine is inactivated New York State Department of Health Human Rabies Prevention - United States, 1999 Recommendations of the Advisory Committee on Immunization Practices (ACIP) Mumps Attenuated MMR Vaccine (requires Acrobat) CDC Measles Attenuated MMR Vaccine (requires Acrobat) CDC Rubella Attenuated MMR Vaccine (requires Acrobat) CDC Influenza Inactivated Copyright 1994 Veterinary Sciences Division Queen's University Belfast CDC Vaccine InformationMMWR, CDC - requires Acribat) Hepatitis A Inactivated Prevention of Hepatitis A Through Active or Passive Immunization: Recommendations of the Advisory Committee on Immunization Practices (ACIP) Hepatitis B Subunit Copyright Dr Linda M Stannard, University of Cape Town, South Africa, 1995. CDC Vaccine Information Varicella Attenuated John Curtin School of Medical Research Australian National University Canberra, Australia. Micrograph: Dr Frank Fenner Prevention of Varicella Updated Recommendations of the Advisory Committee on Immunization Practices (ACIP) Rotavirus Attenuated Copyright 1994 Veterinary Sciences Division , Queen's University, Belfast This vaccine has been linked to higher than normal rates of intussusception - go hereIt is no longer recommended - go hereRotavirus and Intussussception FAQ Yellow Fever Attenuated Yellow Fever Vaccine Recommendations of the Immunization Practices Advisory Committee (ACIP) For more information on anti-HIV (AIDS) vaccines go here HIV/AIDS lecture notes are here

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.

AMH

P.S. I bet this will come up (!)