Dr Warrell qualified at St Mary’s Medical School and worked as a clinical virologist in Oxford hospitals. Her research experience began at the MRC Division of Communicable Diseases at Northwick Park Clinical Research Centre, on the pathogenicity of chlamydiae and mycoplasmas. Later she was a Wellcome Research Fellow at the Bangkok Hospital for Tropical Diseases, Mahidol University, and Deputy Director of the Wellcome-Mahidol University Oxford Tropical Medicine Research Programme while based at the Sir William Dunn School of Pathology in Oxford. Working with Thai colleagues, she studied the pathogenesis and treatment of severe malaria; snake bite; the management and treatment of rabies encephalitis and the economical use of rabies vaccines, notably by multiple-site intradermal application. Her interest in all aspects of the rabies virus and infection continues.
She has been an advisor to the British Medical Association (BMA), the Department of Health and the World Health Organisation (WHO). She is the author of some 80 academic papers and chapters on lyssaviruses in major textbooks.