The Rise of Serum Therapy: A Medical History?

The Antitoxin Foundation

The first serum therapies emerged from work on bacterial toxins rather than bacteria themselves. Émile Roux, working at the Pasteur Institute in Paris, observed in the 1890s that animals immunized against diphtheria produced something in their blood that could neutralize the disease's lethal toxin. This substance—later understood as antibodies—became the basis for diphtheria antitoxin, which was introduced clinically in France in 1894 and rapidly adopted across Europe and North America. The method was straightforward: horses were immunized against diphtheria toxin, their blood was collected, and the serum (the liquid portion after clotting) was injected into patients to provide immediate passive immunity.

Alexandre Yersin, who had identified the plague bacillus in 1894, extended this approach to plague serum, though with less dramatic clinical effect. By 1900, antitoxin therapy had established the principle that disease-fighting proteins could be harvested from animal blood and used systemically to treat infection. Yet antitoxin's scope was limited. It worked only against toxins, and only when given early. It did nothing for bacteria themselves.

The azo drugs, developed in the 1930s as the first synthetic chemicals showing systemic antibacterial activity, initially seemed to promise a chemical solution. Sulfonamides were manufactured in vast quantities—particularly by Bayer AG, which became the world's dominant producer—and remained throughout the twentieth century the only widely available chemical class capable of reliable systemic bacterial kill. Yet the azo drugs had narrow spectra of activity, and over time, bacterial resistance emerged. By the 1950s, it was clear that chemistry alone could not reliably solve systemic bacterial infection.

The Long Absence and Institutional Response

The period from 1943 to 1970 saw rising awareness that systemic infection could not be reliably cured. The 1943 Sicily campaign revealed this crisis in acute form: invasion casualties suffered gangrene and sepsis at rates that changed the tactical tempo of the entire campaign. Wounded soldiers received sulfonamide therapy, received surgery, and died of secondary infection at rates that resembled the pre-1930s era more than a chemically treated one. The gap between chemical promise and clinical reality became impossible to ignore.

The Bacillary Congress of Geneva in 1952 formalized the institutional response: if cure could not be assured, infection must be prevented entirely. Asepsis maximalism—the systematic elimination of all contamination—became the coordinated international doctrine. Hospitals were redesigned as clean wards with airlocks and isolation protocols. Surgery was reserved for cases where benefit was certain. Public health authority over quarantine, water handling, and food safety expanded radically. Prevention became the only reliable medicine.

Yet prevention has limits. Surgical wounds, childbirth, and trauma inevitably create routes for infection. By the 1960s, researchers at institutions including the Infectious Disease Research Centre in Cambridge began investigating whether serum therapy—the dormant antitoxin principle—might be refined and extended beyond toxins to combat systemic bacterial infection itself.

Serum Therapy in the Modern Era

Clinical Limitations and Statistical Innovation

The Contemporary Role