In 1926 the Department of Public Health of the City of Toronto offered immunization with diphtheria toxoid to children in the public schools of the city.1 Such immunization was carried on till June 1929. Advantage was taken of the opportunity to gain an accurate estimate of the efficiency of toxoid in preventing diphtheria in the group so treated. The results of that study, with the methods of calculation, have been published.2 Table 1 presents, in summary, the data of that time. Here the inadequacy of one dose is at once apparent and needs no comment. The advantage of a secondary stimulus in immunization is evident in the much greater reduction of diphtheria (74 per cent) in those given two doses of toxoid. The superiority of three doses is evident in the 90 per cent reduction of cases, with no deaths, in the 16,829 children given three doses of
McKINNON NE, ROSS MA. THE REDUCTION OF DIPHTHERIA FOLLOWING THREE DOSES OF TOXOIDFURTHER OBSERVATIONS. JAMA. 1935;105(17):1325–1329. doi:10.1001/jama.1935.02760430015005
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