[8] In 1890, Kitasato Shibasaburō and Emil von Behring at the University of Berlin reported the development of 'antitoxins' against diphtheria and tetanus.

Their method involved injecting the respective toxins into animals and then purifying antibodies from their blood.

[9] By 1894, the production of antibodies had been optimised with help from Paul Ehrlich, and the treatment started to show success in humans.

[10] The serum therapy reduced mortality to 1–5%, although there were also reports of severe adverse reactions, including at least one death.

Behring won the very first Nobel Prize in Physiology or Medicine for this discovery.

[10] By 1913, Behring had created Antitoxin-Toxin (antibody-antigen) complexes to produce the diphtheria AT vaccine.

In the 1920s, Gaston Ramon developed a cheaper version by using formaldehyde-inactivated toxins.

[10] As the use of these vaccines spread across the world, the number of diphtheria cases was greatly reduced.

In the United States alone, the number of cases fell from 100,000 to 200,000 per year in the 1920s to 19,000 in 1945 and 14 in the period 1996–2018.