Background: We develop a simulation model to study optimal vaccination scheduling for tropical Singapore, assessing the effects of vaccination timing and uptake rate. We then assess the differences in cost-effectiveness under no influenza seasonality, and seasonality of increasing strength modelled upon Singapore, Taipei and Tokyo. Methods: The simulation models heterogeneities in contact networks, antibodies level following infection, the effectiveness of the influenza vaccine and seasonality. Using a no intervention baseline, we consider 3 alternative vaccination strategies: annual and biannual vaccination for a percentage of the elderly and annual vaccination for all elderly and a fraction of the remaining population. Results: In Singapore, annual vaccination for a proportion of elderly are large cost-effective. However, with fixed uptake rates, partial biannual vaccination for the elderly yields a higher ICER than partial annual vaccination for the elderly, resulting in a cost-ineffective ICER. The most optimal strategy is the total vaccination of all the elderly and other age groups, which results in a cost saving ICER. This finding is consistent across different seasonality.