In 1984, Essex identified gp120, the virus surface protein that is used worldwide for blood screening, HIV detection, and epidemiological monitoring.

With collaborators, including African microbiologist Souleymane Mboup, he discovered the first simian immunodeficiency virus, as well as HIV-2.

Essex has worked in twelve (12) different nations as a veterinarian and virologist: Botswana, China, Colombia, India, Japan, Nigeria, Senegal, Taiwan, Tanzania, Thailand, U.S., Zaire.

[4] His 45 years of working papers, the Myron Essex papers, 1949–1996, are archived in the Countway Library's Center for the History of Medicine through funding by a Hidden Collections grant from the Harvard University Library (HUL) within the Maximizing Microbiology: Molecular Genetics, Cancer, and Virology, 1936-2000 project.

In addition to the Myron Essex papers (1949–1996), the project has already led to the processing of collections of several other microbiologists, including those of Bernard D. Davis, Arthur B. Pardee, Francesc Duran i Reynals, and Luigi Gorini.