McLean's research interests are in the use of mathematical models to aid our understanding of the evolution and spread of infectious agents. Her research investigates how quickly infections grow inside individuals, and also how fast they spread amongst individuals.[10]
Following the outbreak in 2001 of foot-and-mouth disease she served as a committee member on the independent review carried out by the Royal Society. The review, chaired by Sir Brian Follett, made recommendations from a scientific standpoint about how to prevent and combat further invasions of highly infectious livestock diseases.
She has continued to serve in an advisory capacity to the UK government, including chairing the lead expert group for a policy futures project on reducing the risk of future disasters, including disease pandemics. She was a member of the Department for Environment, Food and Rural Affairs (DEFRA) Science Advisory Council as well as the Department of Health's National Expert Panel on New and Emerging Infections.[14]
In 2005, McLean also became director of the Institute for Emerging Infections of Humans in the James Martin 21st Century School, Oxford.
From 2013 onwards McLean was involved in the restatement or synthesis of scientific evidence on key topic areas for policy.[15] She co-authored a number of Restatements published by the Royal Society and the Oxford Martin School. The topics included: the health effects of low-level ionising radiation;[16] neonicotinoid insecticides and insect pollinators; the effects of endocrine disrupting chemicals on wildlife; the control of bovine tuberculosis.[17]
During the COVID-19 pandemic in 2020-2021 she attended meetings of the Scientific Advisory Group for Emergencies (SAGE)[19] and was deputy[20] to Sir Patrick Vallance, the Government Chief Scientific Adviser (GCSA). Together with Professor Graham Medley she co-chaired the SAGE sub-committee Scientific Pandemic Influenza Group on Modelling (SPI-M-O).[19] She also contributed to some of the government's media briefings.[21]