In 1897, when Alexandre Yersin was transferred by the Pasteur Institute to a post in Vietnam, his position in Bombay was filled by Simond, who was to test the efficacy of an experimental antiserum against the outbreak of plague in that city.

From 1898 to 1901 Simond served as director of the Pasteur Institute in Saigon organizing a modern vaccine service; he received the distinction of Knight of the Legion of Honour.

From 1901 to 1905 he participated on a mission to study yellow fever in Brazil where he and his colleagues confirmed the results that the U.S. Army Commission led by Walter Reed had just obtained in Cuba.

Simond also had a keen interest in botany; during his stay as a colonial doctor in Indochina from 1914 until 1917, he collected orchids and had a local artist create watercolor paintings of them.

After his death, a fellow biologist, René Dujarric de la Rivière, presented Simond's eulogy at the Academy of Medecine.