Most infectious diseases provoke a response of antibodies which remain forever and leave a “blueprint” in the immune system so that further antibodies can be rapidly made if the germ strikes again.
Thus, one attack of the disease confers lifetime immunity against another attack.
A vaccine is designed to provoke this antibody response without the person getting the disease and suffering its consequences and complications.
The vaccine can be prepared from the toxin or poison of the germ, as in tetanus vaccination.
Other vaccines contain the germ itself, but it’s killed so that it is no longer active. Cholera vaccine is an example.
Others contain the live virus, but attenuated or altered so that, while it still provokes an antibody response, it cannot cause the disease. The measle vaccine is of this type.
Smallpox vaccine is a little different. It contains live virus, not of smallpox but of vaccinia or cowpox. The term vaccine is derived from this word.
The vaccinia virus which causes the mild cowpox is believed to be similar, if not identical, to the virus causing smallpox.
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