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

Live attenuated vaccines play a key role in the control of IB, but limited or no cross-protection confers between serotypes of IBVs. Therefore, it is extremely critical to choose the appropriate IBV vaccines in practice. Little is known about the protection conferred by the commonly used live attenuated vaccines H120, 4/91 and LDT3-A against IBV prevalent local strains in southern China. In the present study, significantly higher antibody levels and percentages of CD4 + , CD8 + T lymphocytes in vaccinated groups compared to the non-vaccinated groups within 21 dpi indicated that the vaccines H120, 4/91 and LDT3-A could stimulate the immunized chickens to produce humoral and cellular immunity that potentially resist or eliminate the infection of IBV. However, at 5 dpc, the protection rates of H120, 4/91 and LDT3-A vaccines against the challenges of the three prevalent IBV isolates were 41.7-58.3%, 75-83.7% and 66.7-75.0%, respectively. Hence, none of the three attenuated vaccines could provide complete protection against all the current prevalent isolates, but vaccine 4/91 offered the best immune protection of the three and vaccine LDT3-A had better protection than the H120 vaccine.