in 1961 he became associate director of the medical and natural sciences division in charge of the rockefeller foundation's arbovirus programme. from 1963 to 1971 he became director of the yale arbovirus research unit and professor of epidemiology. in 1969 he worked on isolating the lassa fever virus with jordi casals-ariet and sonja buckley. he resigned from the rockefeller foundation in 1971 but continued at yale as a lecturer. in 1973 he was appointed clinical professor of epidemiology. the downs fellowship at yale continues his legacy by sponsoring student research in global health. over 600 students have participated in its 50 year history.