He taught at the Johns Hopkins School of Hygiene and Public Health from 1926 to 1938, except for 1930 and 1931, when he served as visiting professor of parasitology at the University of the Philipines in Manila. From 1938 to 1942, Dr. Andrews was director of the Division of Malaria and Hookworm Service of the Georgia Department of Public Health in Atlanta. He was commissioned in the U.S. Public Health Service (PHS) in 1941, and at the outbreak of World War II, joined the Sanitary Corps of the U.S. Army. He was assigned to malaria control activities in the North African Mediterranean and the Pacific Theaters.
After the war, he returned to the PHS as deputy chief and then chief of the Communicable Disease Center in Atlanta. In 1957, he was assigned to the Washington office of the Bureau of State Services.
Dr. Andrews was appointed director of NIAID in April 1957. Under his leadership, the Institute, with the Walter Reed Army Research Institute, established the Middle America Research Unit to study tropical and parasitic diseases in the Canal Zone. Also during this period, studies of the viruses that cause influenza and other acute respiratory diseases in humans dramatically advanced efforts to conquer infectious diseases. NIAID initiated nationwide programs on transplantation immunology and on vaccine and antiviral drug development. Dr. Andrews remained NIAID Director until he retired from the PHS on October 1, 1964. He died June 29, 1967.