Background: Brucellosis remains one of the most widespread zoonotic diseases that primarily affect livestock. Humans generally acquire the disease through eating or drinking contaminated animal products, with the annual incidence of half a million cases globally. In Iran, most regions are endemic for brucellosis that causes not only great economic losses to livestock, but also has a certain public health importance. At present, there is no safe and protective human vaccine against brucellosis, and only several licensed live Brucella vaccines are available for use in livestock included Rev-1 and RB51 vaccines. This study aimed at evaluating the efficacy of vaccination in controlling of brucellosis in livestock and, consequently, in humans in the North and East of Iran. Methods: Sixty-two Brucella spp. isolated from aborted of live stock in two different regions of Iran was used in this study. These samples were collected from Razavi Khorasan and Golestan provinces and biochemical tests were used for identification of Brucella isolates and their information were analyzed by SPSS software v16. Results: In comparison with previous years, the number of aborted in livestock caused by Brucella, demonstrates that despite an increase in vaccination, and not only has not been reduced in the number of brucellosis cases in livestock, but also it has dramatically increased. Conclusion: Increasing brucellosis in livestock and, consequently, in humans, is considered as an alarm in Iran. Therefore, the need for new and improved vaccines along with other factors is necessary more than ever before.

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