Vaccination against Typhoid Fever

The term vaccination was originally used to designate the introduction of material from pustules of cows affected with cowpox into the human being to protect against smallpox. Such produced a mild form of the disease and conferred immunity to the more severe type as represented by smallpox proper. The vaccine represents, then, a weakened or attenuated form of the virus. The term, as now used, applies to the virus of any infectious disease, —the virulence of which virus has been diminished