Empirical studies have found that history of seasonal influenza vaccination [12, [15] [16] [17] [18] , perceived risk of pandemic influenza [17, [19] [20] [21] [22] [23] [24] [25] [26] , worry [17, 22, 26, 27] , and attitudes towards vaccine, such as vaccine efficacy and side-effects [12, 15, 20, [24] [25] [26] were significantly associated with intention to receive a vaccine against the influenza pandemic. This is consistent with the findings related to determinants of vaccination against seasonal influenza [28] [29] [30] [31] [32] . However, there are some common and significant limitations to these empirical studies. First, all except one [24] relied on vaccination intention to predict the actual vaccination uptake. In one study, since only a few respondents reported having received the pH1N1 vaccine, the authors combined those intending to get vaccinated with those who had already received the vaccine into one ''intending'' group and examined factors associated with this 'vaccination intention' [20] . This is problematic because factors associated with vaccination intention and actual vaccination receipt probably differ. Moreover, the reliability of intention as a predictor of actual behavior remains controversial. Harris et al. found that only about half of ''intending'' recipients of seasonal influenza vaccination actually take it and almost all those who do not intend to take it remained unvaccinated [33] . Moreover, most studies conducted before the pandemic occurred or before the vaccine was available [11, 12, [16] [17] [18] [19] 21, 23] of Dutch respondents reported intending to take pH1N1 vaccination prior to or at the onset of the (potential) pandemic phase, respectively [23] . Similarly, in Hong Kong 45% of 301 respondents in July 2009 reported being ''highly likely'' to receive pH1N1 vaccine if offered for free [11, 12] . However, by the time vaccination became available intention appeared much lower with only 10-15% of study respondents in France and in Turkey intending to take the pH1N1 vaccine [20, 24] . Second, all the studies are cross-sectional rather than longitudinal; none assessed subsequent actual vaccination status. Thus, although associations have been identified, there is no way to infer causality. Third, most of the studies are atheoretical. Although some of the studies developed their study questions based on theoretical framework such as HBM [17, 23, 24] , none have conducted model analysis and evaluated the model fit. Therefore, due to these three reasons, there remains a significant concern about how valid such results are and a significant knowledge gap about how the observed pattern of influences could be explained.