We next applied our method to the time series of cases of H5N1 influenza in humans. We produce estimates and credible bounds for R, under different scenarios for the expected fraction of new observed human cases that is attributable to human contagion h. Summary results for Vietnam (and Indonesia) are given in Table 1 . Even in the worst case scenario, where all observed cases are attributed to human transmission (h = 1), the most likely (as of June 2006) R is 0.53 (0.56), with an upper 95% bound of R,0.77 (0.89). For the estimated h = 0.29 (see Methods), the most likely R for both Vietnam and Indonesia is 0, although the estimated upper 95% bound in Vietnam gives the bound R,0.42. For Indonesia, the corresponding estimate gives an R entirely consistent with zero at the 95% credible level.