Dr. Gray has conducted diverse epidemiological studies of infectious diseases for more than 25 years in 5 continents. He has authored more than 425 peer-reviewed manuscripts and book chapters. His published works have been cited by others more than 21,000 times (H-index 76 by Google Scholar).   

Much of his research has involved identifying risk factors for occupational diseases, particularly for respiratory virus infections. He has studied farmers, veterinarians, turkey workers, swine workers, poultry workers, horse workers, cattle workers, hunters, and military personnel.  

He was the original principal investigator for the now ~300,000-person, >24-year Millennium Cohort Study. This prospective cohort study is projected to continue through the year 2068. Dr. Gray was also the principal investigator in a >152,000-person pneumococcal vaccine trial. Currently, he is serving as site principal investigator for a 120-person universal influenza vaccine trail with live virus challenge. 

A strong supporter for the One Health approach, he has won multiple One Health research and training grants, helped to established centers of One Health (USA, Romania, China) and developed four graduate programs in One Health (PhD, MHS, and certificates).   

Dr. Gray has won multiple awards for his research and training: the Department of Defense Legion of Merit Medal for exceptionally meritorious conduct (epidemiological research) for the Department of Defense; the Secretary of Defense Medal for Outstanding Public Service (DoD’s 2nd highest award for a civilian); the University of Iowa’s College of Public Health nominee for University of Iowa’s President and Provost Award for Teaching Excellence; the University of Iowa College of Public Health Faculty Research Award; University of Iowa International Studies Faculty Mentor of the Year; the Medal of Honor from Mongolia’s Minister of Health for health sector development (MoH’s highest award); The Peace Medal awarded by the President of Mongolia for research and prevention of communicable diseases (The Mongolian government’s highest honor for a foreigner); Duke University Department of Medicine’s Excellence in Education Award (Division of Infectious Diseases); Duke University’s Global Health Graduate Professor of the Year; Duke University’s Global Health Graduate Professor of the Year; The American Veterinary Epidemiological Society Honorary Diplomate Award; and the University of Texas Medical Branch Robert E. Shope, MD Professorship in Infectious Disease Epidemiology.  

Professor Gray is a Fellow in the Infectious Diseases Society.