Avian influenza vaccines are commonly used in the poultry industry. The objective of this study was to compare, under experimental conditions, the protective efficacy of four imported commercial inactivated H9N2 vaccines (A, B, C and D) in broiler chickens. A total of 150 one-day-old chicks were divided into six groups: four experimental groups containing each 30 chicks received one of the vaccines (A, B, C, or D) delivered in 0.3ml/dose subcutaneously at one day of age, whereas the control group T was not vaccinated but challenged and the group E was kept unvaccinated and unchallenged. At 21 days post vaccination, groups A, B, C, D and T were challenged with 10 7 Embryo - Infective Dose 50 of A/Chicken/Morocco/01/2016 (H9N2). All chicks were observed daily for clinical signs during the 12 days post challenge (dpc). At 5 and 12 dpc, chicks were humanely sacrificed for necropsy examination. Blood samples were collected weekly for serological analysis and oropharyngeal swabs were collected for virus detection by real time RT-PCR. Respiratory signs started at 48 hr pc and maximum severity was observed on 9 dpc. Especially, the birds vaccinated with vaccine B showed significantly more respiratory signs than their counterparts. Serologic analysis revealed that the sera of Groups A and D birds showed a decrease in antibody (ab) levels up to day 26; then a slight increase of Ab level was observed until day 31, while groups B and C birds showed a stabilization of the titers from day 21 until the end of the experiment. The viral shedding rate was significantly lower in Groups C and A (40-50% of the birds shedding virus for <7 days) compared to other challenged groups (60-75% of the birds shedding virus for ≥9 days). This experiment illustrated that vaccination applied on the first day in the hatchery with the four vaccines tested did not provide an acceptable protection against H9N2 in comparison with the controls that did not receive any vaccine. However, at first glance, we might favor vaccines A and C for their ability to reduce and shorten viral shedding, compared with vaccines B and D.

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