where X and K are the sets of people and locations in the city, respectively; b k is the transmission coefficient associated with a particular location type. The transmission coefficients are estimated such that without any forms of intervention, the proportions of transmissions within the household (P H ), workplace (P W ) and community (P C ) are approximately 30, 37 and 33 per cent, respectively (Ferguson et al. 2006) . This proportion is location-dependent, and the values we followed are reported to be estimated based on data from the United States. Using our transmission coefficients (b h ¼ 1.89 Â 10 21 h 21 , b w ¼ 3.2 Â 10 21 h 21 and b c ¼ 6.51 Â 10 23 h 21 ) the transmission proportions in the model are computed to be P H ¼ 30.7 per cent, P W ¼ 35.6 per cent and P C ¼ 33.7 per cent. G ijk is a proximity function for two individuals x i , x j and location k at a particular time instance. In the model, the function will give 3 if x i and x j are in the same sub-location and 1 if they are in the same location, but different sub-locations. Otherwise it returns 0. I j and S i are parameters that describe the infectiousness of x j and the susceptibility of x i , respectively. The probability of a person getting infected is then given by p(Infected i ) ¼ 1 2 exp(2l i Dt). To simulate external reseeding, we randomly select one person each day and infect him/her with pandemic influenza if he/she is susceptible. For the length of each phase in the transmission model, we did not define a fixed duration. Rather, guided by the values reported in Germann et al. (2006) , we divided the phases into a number of smaller substages, each lasting approximately 5 -6 h. This increases the granularity of the transmission model, and allows us to better scale the infectiousness profile upon consumption of medicine. The smaller substages do not include the susceptible and recovered phases. Hence, given the reported mean lengths of the exposed (1.2 days), pre-symptomatic (0.7 days) and infectious phase (4.1 days), in the model we divided them into 5, 3 and 17 substages, respectively. Simulating the model 20 000 times without any forms of intervention policies or diagnostic approaches gave us an average of 29 h for the exposed phase, 17 h for the presymptomatic phase, and 98.5 h for the infectious phase. Assuming that the total duration of infection follows a normal distribution, we computed the mean length to be 144.5 h and a standard deviation of 6.13 h.