Protective efficacy of single-dose vaccination of rNDV-vectored IBV vaccine candidates in 1-day-old SPF chickens after IBV challenge. A Clinical signs in chickens immunized with the indicated vaccine candidates and challenged with 104.2 EID50 of Egyptian IBV variant strain EG/CU/4/2014. The birds were monitored daily for 10 days for clinical signs scoring (0 = normal, 1 = mild ocular discharge, mild nasal discharge and/or sneezing 2 = heavy ocular discharge, heavy nasal discharge and/or coughing 3 = tracheal rales and/or mouth breathing). Mean score and SEM are plotted for each group. Statistically significant differences versus the control group at each time point are indicated by asterisk. B Determination of viral load by RT-qPCR quantitative analysis of IBV RNA in tracheal and oropharyngeal swabs collected at 5 days post IBV challenge. Each point indicates the viral load for an individual chicken, the lines indicate the mean viral load for each group, and the error bars indicate SEM.