Immunisation in Childhood
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The objective of immunisation is to produce in an individual a degree of resistance equal to that which follows natural infection. This is achieved by introducing into the body viruses or bacteria which have been made non-virulent, but at the same time retaining their antigenic properties. In those cases where the ill effects of the infections are due to toxins, the modified toxin called toxoid is used for vaccination, as in the case of tetanus or diphtheria. With toxoids or where the vaccine consists of killed organisms, several inoculations at regular intervals are necessary to achieve an effective antibody level. On the other hand, where a living organism is used for antigenic stimulation as in the case of smallpox, or B.C.G., one administration may be satisfactory. Both with ‘live’ and ‘killed’ vaccines the antibody level in the blood tends to decline with time, and so ‘booster’ shots are necessary at regular intervals.
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