VACCINATION, the term originally devised for a method of protective inoculation against smallpox, consisting in the in tentional transference to the human being of the eruptive disease of cattle called cow-pox (vaccinia). The discovery of vaccination is due to Dr. Edward Jenner (q.v.), whose investigations were first published in 1798 in a pamphlet entitled An Inquiry into the Causes and Effects of the Variolae Vaccinae, etc. His first case of vaccination (May 1796) was that of a boy, whom he in oculated in the arm with cow-pox matter taken from a sore on the hand of a dairymaid, who had become infected with the dis ease by milking cows suffering from cow-pox. It was apparently in 1798 that he made his first attempt to carry on a strain of lymph from arm to arm.
In applying to cow-pox the term "variolae vaccinae," Jenner expressed his belief that this disease was small-pox of the cow.
As the outcome of much experimental work it may be definitely stated that small-pox lymph, especially if obtained from the pri mary vesicle of a case of the inoculated form of the disease, by passage through the system of the calf becomes deprived of its power of causing a generalized eruption, while inducing at the site of inoculation a vesicle indistinguishable from a typical vaccine vesicle; and, more important still, that when transferred again to man, it has by such treatment completely lost its former variolous character. Such being the case, it is usually considered that cow-pox, or rather that artificially inoculated form of the disease which we term vaccinia, is variola modified by transmis sion through the bovine animal.
The cause of vaccinia is a filter passing virus (q.v.) more re sistant to the germicidal effects of glycerine than ordinary mi crobes. Advantage is taken of this fact, in the method devised by S. Monckton Copeman, and now employed officially in England, on the Continent and in America, for ensuring the bacteriological purity of vaccine lymph.
In 1889 an English Royal Commission on vaccination was ap pointed. The evidence given was published at intervals in a series of Blue-books, and in August 1896 the final report made its ap pearance. As regards the effect of vaccination in reducing the prevalence of, and mortality from, small-pox, the following con clusions were arrived at, with two dissentients: "(I) That it diminishes the liability to be attacked by the disease. (2) That it
modifies the character of the disease and renders it (a) less fatal, and (b) of a milder or less severe type. (3) That the protection it affords against attacks of the disease is greatest during the years immediately succeeding the operation of vaccination. It is impossible to fix with precision the length of this period of highest protection. Though not in all cases the same, if a period is to be fixed, it might, we think, fairly be said to cover in general a period of nine or ten years. (4) That after the lapse of the period of highest protective potency, the efficacy of vaccination to protect against attack rapidly diminishes, but that it is still considerable in the next quinquennium, and possibly never altogether ceases. (5) That its power to modify the character of the disease is also greatest in the period in which its power to protect from attack is greatest, but that its power thus to modify the disease does not diminish as rapidly as its protective influence against attacks, and its efficacy, during the later periods of life, to modify the disease is still very considerable. (6) That re-vaccination restores the protection which lapse of time has diminished, but the evidence shows that this protection again diminishes, and that, to ensure the highest degree of protection which vaccination can give, the operation should be at intervals repeated. (7) That the beneficial effects of vaccination are most experienced by those in whose case it has been most thorough. We think it may fairly be con cluded that where the vaccine matter is inserted in three or four places, it is more effectual than when introduced into one or two places only, and that if the vaccination marks are of an area of half a square inch, they indicate a better state of protection than if their area be at all considerably below this." For the evidence, statistical or otherwise, on which these conclusions are based, the Reports of the Royal Commission should be consulted.