Researched BCG vaccine for tuberculosis, and infant leukemia
Frappier was Professor of bacteriology and chief of laboratories (Hôpital St.-Luc) at the Université de Montréal. He founded the first French language institute of hygiene in the world, l'Institut de microbiologie et d’hygiène de Montréal, renamed l'Institut Armand-Frappier in 1975.
Frappier studied tuberculosis and BCG (bacille Calmette-Guérin) vaccine. He was one of the first North Americans to confirm the safety and efficacy of BCG as a vaccine for tuberculosis and to develop ways to study and use it. He showed it also had preventative effects in cases of infant leukemia. In addition, he studied the mechanisms of infection and of resistance to certain infections.