A robust theoretical framework comprehensively explaining behavior change that elucidates population decision-making for health protective and promoting behaviour has long been sought. As the main contender, the TPB explains ,34% of variance in health behavioural change related to addictive behaviour, automobile-related behaviours, clinical and screening behaviour, eating behaviour, exercising behaivour, HIV/AIDS-related behaviour and oral hygiene behaivour [40] . The standard version of TPB proposes that attitudes towards the behaviour, subjective norm and PBC predict behavioral intention while intention and PBC predict the actual behavioural change [38, 39] . Additional predictors that significantly improve the model's predictive power are needed [39] . Two previous studies have examined modified versions of TPB to predict vaccination uptake against seasonal influenza [50, 51] . One study used TPB plus two additional factors: influenza vaccination history and anticipated regret, to predict intention to receive vaccine against seasonal influenza among elderly from social clubs [50] : vaccination history and anticipated regret respectively accounted for an additional 10.7% and 13.7% of total variance in influenza vaccination intention [50] . However, again the study was cross-sectional and actual vaccination uptake was not assessed. A second study of healthcare workers [51] adopted an extended version of TPB that included additional elements of anticipated regret, moral norm, descriptive norm and professional norm. The study found that controlling for the original TPB variables, moral norm and anticipated regret were significant determinants of actual receipt of seasonal influenza vaccine [51] . The study provides useful information for future application of the extended version of TPB. However, since the study was conducted among healthcare workers, some of the variables such as moral norm and professional norm which emphasize obligation and professional convictions may not be applicable among the general population.