Semple has studied severe virus disease outbreaks since 1989 in the field of diagnostics, clinical characterization and clinical trials. He was a founder member of ISARIC. He has led studies of COVID-19, MERS, Monkeypox, Ebola (EVD and Survivors), Influenza and Bronchiolitis, at times field-deployed in austere circumstances. He is a Senior Government Clinical Advisor siting on the Scientific Advisory Group for Emergencies (COVID-19 response) and the New Emerging Respiratory Viral Treats Advisory Group (NERVTAG), and former member of the WHO Scientific Technical Advisory Committee for Ebola Emergencies (STAC-EE), Gov.UK Pandemic Flu group. He was appointed Honorary Respiratory Physician at Alder Hey Children’s Hospital Liverpool in 2006. In 2016 he and his team were awarded the Queen’s Ebola Medal for Service in West Africa 2014-16 and in 2019 he received a Commonwealth Association Award for subsequent work with Ebola survivors in Sierra Leone.