During World War II, Dr. Haas was chief of the Medical Commission to the Yunnan-Burma Railway in China and staff officer in the China-Burma-India Theater. He was the officer in charge of PHS malaria investigations from 1943 to 1948.
As first director of the National Microbiological Institute (NMI), Dr. Haas established programs to fund research conducted by scientists outside NIH and to support young investigators through training and fellowship grants.
During this period, scientists developing diphtheria and tetanus antisera observed that some patients exhibited severe hypersensitivity reactions to horse serum injections. This evidence of an immune system gone awry signaled that the Institute should include basic studies of the immune system in its future plans. To acknowledge the NMI expanded mission, it was renamed the National Institute of Allergy and Infectious Diseases in 1955. Dr. Haas was NIAID director until he retired from the PHS on January 1, 1961.