For 42 years, Dr. Levine has conducted Phase 1, 2, 3, and 4 clinical trials to evaluate the safety, immunogenicity, and efficacy of a wide array of vaccines; served as a clinician in vaccine testing for both adults and children; designed and supervised domestic and international epidemiologic studies; overseen research activities in the laboratory; and supervised development of diagnostic assays for use in developing countries and subsequent testing in field trials. His laboratory research has focused on the construction and characterization of attenuated strains of Salmonella Typhi, S. Paratyphi A, non-typhoidal Salmonella serovars, and Shigella to serve as live oral vaccines and as live vectors for the expression of foreign antigens. Multiple constructs have progressed from animal models to human trials. Dr. Levine has designed and supervised large-scale, randomized, controlled field trials that investigated the efficacy of live oral typhoid vaccine Ty21a, which led to its licensure by the US Food and Drug Administration (FDA). Post-licensure work with Haemophilus influenzae type b conjugate vaccine led to early introductions into the routine infant immunization schedule in Chile (1996) and Mali, West Africa (2005). After years of challenge trials and an effective clinical trial, the single-dose oral cholera vaccine, Vaxchora, was approved for licensure by the FDA in 2016.