Newcastle disease causes many economic losses to the poultry industry in most countries. This disease is endemic in Iran. Backyard poultry is considered the reservoir of Newcastle virus; however, there is either no vaccination program against Newcastle, or it is performed in a restricted manner. Commercial live vaccines are inactive and sensitive to temperature; moreover, vaccine delivery to villages and remote areas requires special equipment and high cost to maintain the cold chain. This study evaluated the effectiveness of a thermostable Newcastle vaccine produced by the Razi Institute (ND.TR.IR) on the backyard poultry. In four provinces, at least 4 villages were selected as the treatment group, and the same number was selected as the control group. At least, 30 birds were sampled in each village. In each group, blood samples were collected before vaccination and 2 weeks later, and the serum titer of the samples was examined with the haemagglutination inhibition test. The arithmetic mean and standard deviation of the sample titers at the rural level were compared using paired t-test before and after vaccination in each group. Moreover, Repeated Measures ANOVA was utilized to compare the vaccinated and control groups in terms of the titer changes before and after vaccination. In this study, 584 and 389 samples were taken from the treatment (53 households in 20 villages) and control groups (33 households in 14 villages). The mean serum titer values of Newcastle were 4.51±3.03 and 6.64±2.48 in the treatment group before and after vaccination, respectively (P<0.001). The increase in mean titer of the treatment group (2.31 log) was statistically higher than that in the control group (0.66 log) (P<0.001). Out of 584 birds, 517 (88.5%) ones had titer above 3 in the second turn in the treatment group. The thermostable vaccine (ND.TR.IR) produced by the Razi institute is suitable for backyard poultry, which immunizes them against Newcastle disease. Appropriate vaccination programs for backyard poultry should be made; moreover, vaccination of backyard poultry can be effective in preventing the circulation of the field viruses.

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