Study in the Epidemiology of Diphtheria in Relation to the Active Immunization of Certain Age Groups

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Abstract
Injection of 50-70% of children more than 5 yrs. old, with 3 doses of toxin-antitoxin has failed in numerous instances to produce any marked effect on diphtheria incidence in a community. Immunization of 30% or more of children under 5 yrs. old, in addition to more than 50% of those 5-9 yrs. old, has in several instances produced an immediate and striking decline in the diphtheria rate of a community. The promptness of this seeming response suggests that a high degree of immunity is quickly acquired by a majority of those given 3 doses of toxin-antitoxin; it is a matter, probably, of a few wks. rather than of several mos. In only 2 instances known to the author has a community, that had attained 30% immunization of the age group under 5 yrs., suffered even a moderate epidemic. It is possible that immunization of this group should not be uniformly distributed through the community but should be largely concentrated in sections of highest prevalence, if diphtheria is prevalent; if not, then in the congested areas. The study is presented as a working hypothesis, worthy of trial as a means of quickly ridding a community of epidemic diphtheria; more data from more varied sources are necessary to establish its validity. To this end, uniformity in tabulation of immunization statistics is necessary. The Committee on Administrative Practice and all health departments should adopt the standard age grouping in their tables, should classify immunizations by single yrs. of age up to 10 yrs., and should annually or oftener so tabulate their material as to show the present status. It is suggested that unrecognized cases rather than healthy carriers are responsible for occult infections occurring during epidemics or periods of high prevalence. It seems not improbable that many mild nasal cases would be discovered if diligently sought; such cases are the ones most likely to spread infection. It should be clearly understood that the author makes no plea for any community to stop work when it has attained a 30% immunity. Active immunization, like antitoxin, was introduced on a wholesale scale during a period when diphtheria was receding from a period of high epidemicity; it is the more difficult, therefore, to measure its effect. The immunity conferred may not suffice for an organism of greater invasiveness, virulence and pathogenicity. In any event, the only reasonably-sure protection for the individual is individual immunization. The records of 10 cities in New York are shown graphically and discussed in the text.

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