The present study was conducted to estimate the breadth of the protection against the characterized Egyptian (EG/1212B) strain of IBV and evaluation of different immunization programs using some available commercial live vaccines in Egypt as following; group (1) vaccinated by (IB Primer and Ma 5), group (2) vaccinated by (IB Primer and 4/91), group (3) vaccinated by (Ma5 and H120), group (4) are non-vaccinated challenged and group (5) are non-vaccinated non-challenged. At 26th days, the chickens in groups (1,2,3 & 4) were individually challenged with (105 EID50/bird) IBV (EG/1212B) strain. The results indicated that group (1) recorded the highest degree of ciliary protection by 82%, followed by the second group by 56%, then the third group by 32% in relation to control non-vaccinated non-challenged group (5). Groups No. (1, 2, 3 and 4) secreted the challenge virus at 5days PC at different rates and group (1) had the lowest rate of virus secretion. Group (2) recorded the highest serological response to vaccination at 26th days (day of challenge) with 80% positive random samples. Experimentally challenged chicks showed varying degrees of coughing, sneezing, tracheal rales, head shaking, depression and watery feces. No mortalities were recorded in all five groups. The main common lesions were swollen and congestion of kidneys together with tubules and ureters distineted by urate. There were sticky clear mucoid secretion in orophraynx and trachea of groups (2, 3 and 4). Histopathological finding PC, exhibited tracheal lesions of varying degree of deciliatin, thickning in lining epithelium accompanied with inflammatory cells infiltration and vacuolation of goblet cells. In addition to renal lesions with varying degree of focal interstitial nephritis and hydrobic degeneration. The impact of the three immunization programs on the rate of body weights gain of vaccinated birds at 26th days (day of challenge) and at 7 days PC had recorded.
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