Infectious diseases such as influenza and dengue have the potential of becoming a worldwide pandemic that may exert immense pressures on existing medical infrastructures. Careful surveillance of these diseases, supported by consistent model simulations, provides a means for tracking the disease evolution. The integrated surveillance and simulation program is essential in devising effective early warning systems and in implementing efficient emergency preparedness and control measures. This paper presents a summary of simulation analysis on influenza A (H1N1) 2009 in Malaysia. This simulation analysis provides insightful lessons regarding how disease surveillance and simulation should be performed in the future. This paper briefly discusses the controversy over the experimental field release of genetically modified (GM) Aedes aegypti mosquito in Malaysia. Model simulations indicate that the proposed release of GM mosquitoes is neither a viable nor a sustainable control strategy. Keywords: dengue, A H1N1, GM mosquitoes, simulation. 1 Introduction The World Health Organization (WHO) announced on 11 June 2009 that the influenza A (H1N1) has reached the stage known as pandemic alert phase 6 with moderate severity. On 10 August 2010, WHO declared that pandemic alert phase 6 for A (H1N1) is officially over and the world has entered into the post pandemic period. However, the looming threat of another A (H1N1) pandemic