Influenza is a common infectious disease affecting 5%-10% of adults and 20%-30% of children. There are an estimated 3 to 5 million cases of severe influenza-related illness worldwide each year, and 250 000 to 500 000 deaths (WHO, 2014). Influenza can also have a major impact on health care systems. In the United States, it is estimated that each year, more than 200 000 people are hospitalised for respiratory and heart condition illnesses associated with seasonal influenza virus infections (Thompson et al., 2004). At certain times of the year, influenza can place health systems under significant stress. For example, in Ontario, Canada, the average annual rate of emergency department visits attributable to seasonal influenza is 500 per 100 000 population. This rate increased to an estimated 1 000 per 100 000 population during the H1N1 pandemic in 2009 (Schanzer et al., 2013).