Significant health promotion activities regarding influenza prevention have been prominent in Hong Kong since well before the onset of pH1N1, arising largely from the Severe Acute Respiratory Infection (SARS) epidemic and A/H5N1 Bird Flu outbreaks. Seasonal influenza vaccination is widely promoted each year. Hong Kong's pH1N1 epidemic started on 11 June 2009, peaking in September, and by early November had petered out ( Figure 1 ). By the end of December 2009, the Hong Kong government had recorded 37,174 human pH1N1 cases [8] in a population of ,7 million. To minimize any potential second wave, significant televised and other publicity was given to the launch of a pH1N1 vaccination programme on 21 December 2009, initially for five priority groups: healthcare workers, persons with chronic illness and pregnant women, children aged 6 months to 6 years, adults aged 65 years or above, and pig farmers and slaughtering industry personnel [9] . On 26 January 2010 pH1N1 vaccination was extended to the general public. The vaccination was free for priority group members [10] , but cost HK$100-150 (US$13-20, 1-1.5% of Hong Kong's median monthly income of HK$10,000/ US$1,286/J991) per dose for the general population. A study in July 2009 of 301 respondents projected that vaccine uptake would be influenced by end-user cost, with 45%, of Hong Kong's general population being ''highly likely'' to take up pH1N1 vaccine if free, and 24% if costing HK$100-200 (US$ [13] [14] [15] [16] [17] [18] [19] [20] [21] [22] [23] [24] [25] [11, 12] .