ABSTRACT
Effective reproductive number [Re] is an index which considers the proportion of susceptible people in a community. There are different methods for calculation of basic reproductive number. The aim of this study was to evaluate the reproductive number using data from H1N1 patients in Fars Province, southern Iran. According to the data obtained, 233 cases were confirmed between July 15[th] and December 3[rd], 2009 Two waves were observed during this period with a peak in October 21[st] in Fars Province. In the first wave, the highest amount of Ro was 3.22 and the lowest amount was 2.12 and in the second wave, the highest and lowest amounts of Ro were 3.42 and 2.42, respectively. Effective reproductive number could not be more than 1.54. Thus in order to maintain Ro below 1, using preventive measures like vaccination, only 70% of population should be immune. As 54.9% of Fars population were immune against H1N1 if only 15.1 of them take part in vaccination program, the disease will not reach an epidemic level