How it began
During a yellow fever outbreak in Dakar in 1927, Jean Laigret, working with Constant Mathis of the local Pasteur Institute and Harvard researcher A. W. Sellards, took blood from a patient, Francois Mayali, who had a mild case. The blood produced severe yellow fever in a rhesus monkey, and the virus became known as the French strain. Passed repeatedly through mouse brain, it yielded the French neurotropic vaccine strain around 1930. The Institut Pasteur in Dakar then developed and produced the vaccine.
How it works
The vaccine was a live virus weakened by serial passage in mouse brain; sources give 128 or 260 passages. It was prepared from infected, dried mouse brain that was reconstituted and applied by scarification, scratching it into the skin. From 1939 the mouse-brain vaccine was given by scarification alone or together with smallpox vaccine, a method reported by Peltier and colleagues from trials in Senegal in 1940.
Who pushed back
The strain remained neurotropic, and neurologic reactions became more evident after World War II. Rates of post-vaccinal encephalitis in children were judged unacceptable, and in 1960 use was restricted to people over 10 years of age. The rival 17D vaccine, developed at the Rockefeller Foundation from the Asibi strain, proved safer.
What changed first
The vaccine was administered extensively in French-speaking Africa starting in 1940, and more than 84 million doses were distributed in French West Africa between 1940 and 1954. A World Health Organization review states that yellow fever virtually disappeared from colonial French West and Equatorial Africa as a result of a compulsory immunization program begun in the early 1940s.
Where it stands today
Production of the French vaccine was discontinued in 1982, and since then 17D has been the only yellow fever vaccine in use. The Institut Pasteur in Dakar went on to produce 17D vaccine following methods recommended by the World Health Organization. Archived samples of the Dakar strain are still studied; a 2018 sequencing study found evidence that it was genetically unstable.
