From the French influenza study [10] , I obtain maximum likelihood estimates of the within household transmission parameter of r n = 1.35/n 1.0 (which is consistent with the best fit to the Tecumseh data [8] of r n = 1.27/n 0.97 ). The former study followed seronegative households for a two week winter outbreak of seasonal influenza. The corresponding escape probabilities are Q 2 = 50.9% (i.e. the probability of not being infected by the other household member in a household of size two is 50.9%), Q 3 = 63.8%, Q 4 = 71.4%, Q 5 = 76.4% and Q 6 = 79.9%. On the scale of other infections, this places influenza as being approximately as infectious as mumps, but a lot less infectious than either varicella-zoster or measles [1] . By applying the Reed-Frost model to these data with this distribution of households, I obtain estimates of the average number of infections in each generation of infection of m 1 u 1, m 2 = 0.64 (i.e. the first index case directly infects an average of 0.64 people in his or her household), m 3 = 0.19, m 4 = 0.036, m 5 = 0.0037 and m 6 = 0.00021, and thus the estimate for the total expected number of cases in an infected household is m = S 6 i = 1 m i = 1.87, to be compared to the mean size of 3.06. These calculations are performed in Microsoft Excel 2007 using equation (25) .