Abstract
During the past years, we have immunized a series of guinea pigs and a series of horses and a series of children with diphtheria toxin-antitoxin mixtures. The duration of the immunity presents certain points of great interest. So far as our observation goes, guinea pigs are never naturally immune; horses in the very great majority of cases are immune; adults and infants under 6 months are immune to 80 per cent., while very young children are nonimmune to about 60 per cent. We find, in the guinea pig, that active immunity lasts for about nine months. In horses, we find the increased immunity, due to the injections, lasts from nine months to twelve months, at which time the horses return to their original amounts of natural antitoxic immunity.
In testing human beings from month to month, it was a matter of great interest to find whether the infants and children who become immune, due to the injections, would, like the guinea pigs, lose their immunity in about nine months or whether the active immunity would be replaced by natural immunity just as in the majority of infants the stage of lack of immunity is followed by antitoxic immunity. We have found, in infants, two years after successful immunization that the great majority have remained immune, not over 6 per cent. losing their immunity. We have a right, therefore, to hope that the stimulated immunity has been replaced in the very great majority by a natural immunity and that this will hold for life. The facts that the protection lasts and that the injections are harmless make the active immunization of infants appear to be a practical measure of eliminating diphtheria.
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