The H1N1 influenza pandemic caused more severe health impacts for Maori and Pacific peoples, with markedly higher hospitalisation and intensive care unit (ICU) admission rates for these ethnic groups compared with Europeans and others. This project will investigate whether infection rates (seroprevalence) showed the same differences as disease rates, and the contribution of chronic illnesses (such as asthma and diabetes) to the risk of infection and to poor outcome (ICU admission and/or death). It will also analyse the contribution, to health impacts, of environmental factors (including household crowding, housing conditions, and environmental tobacco smoke exposure) and differences in how groups responded to influenza (including measures to avoid infection, recognition of illness, health-seeking behaviour, and attitudes to vaccination). The goal is to identify opportunities for reducing these inequalities. Such measures could help protect vulnerable populations during future waves of this pandemic as well as reduce rates of infectious disease more generally.