How did diphtheria immunization reduce deaths in New York City?

Diphtheria immunization significantly reduced mortality in New York City and elsewhere by transitioning from reactive treatment to proactive prevention. Initially, the New York City Health Department began producing and testing diphtheria antitoxin in 1895, which helped treat active cases. However, while antitoxin reduced the death rate among those already infected, it did not significantly lower the overall number of cases.12

The dramatic decline in disease prevalence and deaths was achieved through mass immunization programs. In 1914, William H. Park developed a toxin-antitoxin mixture for immunization, which was later superseded by the more effective diphtheria toxoid developed by Gaston Ramon in 1923. As widespread immunization of children with the toxoid became standard practice, the incidence of the disease and subsequent deaths became almost nonexistent. Today, this protection is maintained through routine childhood vaccination schedules, typically administered as part of the DTaP vaccine.2134