Rabies Shots - 1 or 3 Years?

I have always wondered how a rabies vaccine could be good for 1 or 3 years. If it is stimulating the immune system to produce antibodies, how would one last longer than the other? It can't be a time released thing in the body, can it?

Actually it is a time released thing in the body. :-) This effect has to do with something called the "depot effect". In commercial vaccines, modified-live virus vaccines seem to produce stronger reactions and longer immunity. However, even amongst inactivated vaccines (killed) there is the variable response.

This has to do with something called "adjuvants" that are present in the vaccine. A vaccine is not simply a liquid form of killed virus in water but is a slurry of vaccine and other chemical agents. If you kill the virus, the body produces an immune response to the antigen but it can be very weak (since the virus is already dead) and not provide a long-standing immunity. Drug companies have found that you can add certain chemicals to the mixture (like aluminum salt), and they will sequester portions of the vaccine component, slowing its release to the body. This is the sort of "time release" we are famililar with in our cold medications. The adjuvants then act as a "depot" for the vaccine, as it released slowly into the dog's circulation from the site of the injection. This gives the lengthened time of immune response and the difference between vaccine immunity protection times. Different adjuvants give different immune times, and also different side effects. These adjuvants are what normally produce the most side effects associated with vaccines (other than the slight possibility of contracting the disease from modified-live versions).

There are also new adjuvants that utilize an increased production of cytokines to provide strengthened immunity.

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