en تخصصي Special پژوهشي Original article <div><strong>Background and Aims:</strong> Avian influenza (AI) is an acute infectious disease of poultry, waterfowl, wild birds, and animals, zoonotically transmitted to humans. Some incidents of HPAI are reported in Iran: H5N1 and H5N8. Iranian Veterinary Organization decides on vaccination (H5) of layer and breeder flocks in high-risk provinces following the outbreak in Iran. This study aimed to evaluate the serum response of the vaccine in the layer flocks of high-risk provinces.<br> <strong>Materials and Methods:</strong> Ten laying farms (Size: 30000-50000) were selected from Qazvin (no: 2) and Isfahan (no: 8) provinces that received the H5 vaccine (Four farms: 1 time; 6 farms: 2 times of vaccine shots). Twenty-five blood samples were taken from each flock. The HI test was carried out in a U-bottomed microtiter plate and 4 HA units of homologous antigen.<br> <strong>Results:</strong> The mean titers of antibodies in the poultry farms that received the vaccine once were 1.87, while those that received the immunization twice were 4.90 (significant difference; p<0.05). Also, if we consider protection baseline 4, 4 out of 6 flocks (~67%) could make it above it. Injection of the vaccine twice also improved CV.<br> <strong>Conclusion: </strong>In combination with other control measures such as good biosecurity and monitoring programs, vaccination is considered a suitable and powerful tool to support AI eradication or control programs in endemically infected countries if the Iranian Veterinary Organization (IVO) did regular post-vaccination surveillance and evaluated the flocks for silent infections.</div> Avian Influenza, H5, Iran, Layer, Vaccination 26 31 http://journal.isv.org.ir/browse.php?a_code=A-10-120-13&slc_lang=en&sid=1 Hossein Hosseini hosseini.ho@gmail.com 10031947532846007230 10031947532846007230 No Department of Clinical Sciences, Faculty of Veterinary Medicine, Karaj Branch, Islamic Azad University, Alborz, Iran Mohammad Hossein Fallah Mehrabadi mhf2480@yahoo.com 10031947532846007231 10031947532846007231 No Razi Vaccine and Serum Research Institute, Agricultural Research, Education and Extension Organization (AREEO), Tehran.Iran Ali Tolooe Zarrin atolooe@gmail.com 10031947532846007232 10031947532846007232 No Department of Microbiology and Immunology, University of Tehran, Faculty of Veterinary Medicine, Tehran, Iran. H Haghbin Nazarpak 10031947532846007233 10031947532846007233 No Department of Clinical Sciences, Faculty of Veterinary Medicine, Karaj Branch, Islamic Azad University, Alborz, Iran Reza Khaltabadi Farahani rezafarahanikh@yahoo.com 10031947532846007234 10031947532846007234 No Iranian Veterinary Organization, Tehran, Iran R Farahani 10031947532846007235 10031947532846007235 No Iranian Veterinary Organization, Tehran, Iran Saeedeh Abbasian ghalyanchilab@gmail.com 10031947532846007236 10031947532846007236 No Department of Microbiology and Immunology, University of Tehran, Faculty of Veterinary Medicine, Tehran, Iran. Ali Hojabr Rajeoni 10031947532846007237 10031947532846007237 No Department of Microbiology and Immunology, University of Tehran, Faculty of Veterinary Medicine, Tehran, Iran Zahra Ziafati Kafi 10031947532846007238 10031947532846007238 No Department of Microbiology and Immunology, University of Tehran, Faculty of Veterinary Medicine, Tehran, Iran Naser Sadri 10031947532846007239 10031947532846007239 No Department of Microbiology and Immunology, University of Tehran, Faculty of Veterinary Medicine, Tehran, Iran Arash Ghalyanchi langeroudi arashghalyanchi@gmail.com 10031947532846007240 10031947532846007240 Yes Department of Microbiology and Immunology, University of Tehran, Faculty of Veterinary Medicine, Tehran, Iran.