where m i~Rt ( P k j~1 p j N i{j ). Parameter estimates are obtained using maximum likelihood methods. For this method we used 6 days as the maximal value of the SI (k), which is consistent with the length of the SI observed in field investigations in South Africa [22] . In addition we implemented a sensitivity analysis to assess the variation of the initial R t estimates vis-à-vis k values of 4 days and 8 days, respectively.