In 1886, Yersin entered Louis Pasteur's research laboratory at the École Normale Supérieure, by invitation of Emile Roux, and participated in the development of the anti-rabies serum.

He joined the recently created Pasteur Institute in 1889 as Roux's collaborator and discovered with him the diphtheric toxin, produced by the Corynebacterium diphtheriae bacillus.

[5] The plague bacillus develops better at lower temperatures, so Yersin's less well-equipped lab turned out to be an advantage in the race with Kitasato, who used an incubator.

This important discovery was communicated to the French Academy of Sciences in the same year, by his colleague Emile Duclaux, in a classic paper titled "La peste bubonique à Hong-Kong".

He opened a new station at Hon Ba in 1915, where he tried to acclimatize the quinine tree (Cinchona ledgeriana), which was imported from the Andes in South America by the Spaniards, and which produced the first known effective remedy for preventing and treating malaria, a disease which prevails in Southeast Asia to this day.

On 8 January 1902, Yersin was accredited to be the first Headmaster of Hanoi Medical University by the Governor-General of French Indochina, future president of France Paul Doumer.

Following the country's independence, streets named in his honor kept their designation and his tomb in Suoi Dau was graced by a pagoda where rites are performed in his worship.

[8] His house in Nha Trang is now the Yersin Museum, and the epitaph on his tombstone describes him as a "Benefactor and humanist, venerated by the Vietnamese people".