Immune protection conferred by three commonly used commercial live attenuated vaccines against the prevalent local strains of avian infectious bronchitis virus in southern China

FAN, Wen-Sheng; LI, He-Ming; HE, Yi-Ning; TANG, Ning; ZHANG, Li-Hua; WANG, Hai-Yong; ZHONG, Lian; CHEN, Jian-Cai; WEI, Tian-Chao; HUANG, Teng; MO, Mei-Lan; WEI, Ping

According to the requirements in China, the clinical protection offered by a compliant IB vaccine must be not less than 80% against a virulent challenge [13] . Previous studies demonstrated that the H120 vaccine couldn't provide sufficient protection against the field isolates in China [6, [13] [14] [15] 24] . The latest report showed that a novel recombinant virulent IBV strain was isolated from an H120-and 4/91-IBV-vaccinated flock in China [27] . In our study, the attenuated vaccine 4/91 could not provide complete protection against IBV GX-NN09032 strain even though they shared the same serotype [20] . The reason for this may be that a single vaccine dose of a monovalent vaccine could not provide sufficient immunity with complete protection to birds. Therefore, in an attempt to provide broader protection to chickens, the prime-boost vaccination program in combination with application of two different IBV vaccines ("live + live" or "live + inactivated") should be performed for the birds in southern China. In other countries, it has also been showed that vaccination with two antigenically distinct live-attenuated vaccines can achieved a broad cross-protection against multiple different IBV types [5, 21, 22] . Further investigation will be necessary to determine which combination of H120, 4/91 and LDT3-A vaccines could provide the most effective protection against the prevalent local strains in southern China.