During World War I he was a doctor of colonial troops, receiving the Croix de Guerre in 1916.
Beginning in 1898 there had been sporadic outbreaks of the plague in the country, and none of the previously developed vaccines were strong or durable enough to handle the disease.
In the 1930s, Girard and his assistant, Jean Robic developed an anti-plague vaccine known as the "EV strain".
The EV strain had excellent results against the plague, and inoculation was carried out by Colonial Army medical officers and auxiliary Malagasy physicians.
In 1941 he succeeded Edouard Dujardin-Beaumetz (1868-1947) as director of plague services at the Pasteur Institute in Paris.