Onset of fatal yellow fever illness

On August 18, 1901, Clara Maass fell seriously ill with yellow fever after undergoing repeated experimental inoculations via infected mosquito bites as part of the ongoing Havana yellow fever research program, by then continued under Dr. William Gorgas and colleagues following Walter Reed's initial commission.

Maass had already survived one earlier, milder bout of the disease from a previous experimental bite, and researchers had hoped that her prior infection might have conferred immunity — a hypothesis under active investigation at the time regarding whether survivors of yellow fever gained lasting protection. Tragically, this final inoculation proved catastrophic, triggering a severe and rapidly progressing case of the disease.

Her condition deteriorated quickly, marked by the hallmark symptoms of severe yellow fever: high fever, jaundice, internal hemorrhaging, and liver failure. The sudden severity of her illness alarmed the medical team overseeing the experiments and drew increasing public and press scrutiny to the ethics of continuing human trials, particularly involving female volunteers.

This onset of illness marked the beginning of the end of the Havana mosquito experiments involving human volunteers; her suffering and subsequent death six days later became a pivotal, sobering moment that intensified debate over the moral boundaries of using human subjects — especially women and civilians — in dangerous infectious disease research, a debate whose echoes persist in modern research ethics.