Helen Weiss is an epidemiologist at the London School of Hygiene and Tropical Medicine (LSHTM), where she is joint Head of the Department of Infectious Disease Epidemiology. Dr Weiss gained an MSc in Medical Statistics and DPhil in Cancer Epidemiology at the University of Oxford, studying the long-term effects of radiotherapy. Following postdoctoral work at the US National Cancer Institute, she joined the LSHTM in 1997. Since then, Dr Weiss research has focused on HIV epidemiology in sub-Saharan Africa, working observational studies and randomized controlled trials of behavioural and biomedical HIV prevention strategies. These have included the multicentre study of factors associated with the differential spread of HIV in sub-Saharan Africa, and trials of the impact of herpes suppressive therapy on HIV acquisition, educational interventions in young people, and the impact of episodic herpes treatment on HIV infectivity. Dr Weiss has co-authored more than 150 peer-reviewed scientific publications, including a series of systematic reviews on the role of male circumcision for HIV/STI prevention.