Second experimental mosquito bite

In May 1901, Clara Maass submitted to a second round of mosquito-bite exposure as part of the continuing yellow fever experiments in Cuba. Researchers, working under the direction of figures such as Major William Gorgas, were attempting to determine whether repeated controlled exposure could confer lasting immunity to yellow fever without triggering a severe, potentially fatal case of the disease.

This second bite came after Maass had experienced only a mild reaction to her first exposure in March, which likely encouraged both her and the researchers to continue the trials. The experiments were part of a broader, historically significant effort to conclusively prove the mosquito-vector theory of yellow fever transmission, first advanced by Cuban physician Carlos Finlay and later validated by Walter Reed's Yellow Fever Commission.

Maass's repeated participation illustrates the era's reliance on human volunteers — often nurses, soldiers, or paid subjects — in medical research long before the establishment of modern informed-consent standards and ethical review boards. Her continued involvement, motivated in part by a modest financial stipend and a strong sense of duty, foreshadowed the tragic outcome that would follow after subsequent exposures. Each bite added incrementally to the body of evidence used by researchers to argue that yellow fever could be controlled through vector eradication rather than treatment of the infected.