noun, masculine/vak.sɛ̃/plural: vaccins
vaccine (substance that stimulates production of antibodies)
“Un vaccin est une préparation biologique administrée à un organisme vivant afin de stimuler son système immunitaire et de développer une immunité adaptative protectrice et relativement durable contre l'agent infectieux d'une maladie particulière.” — A vaccine is a biological preparation administered to a living organism in order to stimulate its immune system so that it develops an immunity which is adaptive, protective, and relatively durable against the infectious agent of a particular illness.
Remade as a masculine noun from vaccine, based on Latin vaccinus, where vaccine was also ultimately borrowed from (through a New or Scientific Latin variola vaccīna, "cowpox").