Vaccines : What’s in them and how do they work?

A vaccine stimulates a specific immune response in an animal to give them protection against disease. The way a vaccine does this is by “tricking” the animal into thinking it is being infected, so it makes the appropriate antibodies. This means when the animal is actually exposed to the “real disease” it already has the appropriate immune response ready to roll which should prevent, or reduce the impact of, the disease in the animal. Vaccines are able to do this as they contain the actual virus or bacteria responsible for the disease. This part of the vaccine is called the antigen.

For some diseases we need the vaccine to contain a “live” antigen. These “live” vaccines contain a strain of bacteria or virus that has been modified in the laboratory so it will actively infect and replicate in the animal, stimulating a strong immune response, but it still cannot actually cause the disease. Examples of vaccines which are mostly “live” are PRRS vaccines.

However, often in these “dead” vaccines there will be a substance included called an adjuvant. Adjuvants are wide-ranging in composition, for example inorganic salts, animal oils, or mineral oils, but all are designed to carry the antigen and essentially act as an irritant, attracting the immune system to focus on the site of vaccination so it responds strongly to the antigen within the vaccine. Care should be taken when administering any vaccine, but particular care should be taken with handling vaccines containing mineral oil adjuvants as partial amputation of digits has occurred in several cases of nasty human self-injection!

Vaccines are becoming increasingly important. Although they can be an expensive purchase, an effective vaccine, administered properly, should always give you a good economic return on investment.

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