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

A previous report showed that the best protection against challenge is achieved by a vaccine containing a homologous strain [7] . In this study, the attenuated vaccine H120 (serotype 3) provided poor protection against IBV GX-YL5 (serotype 1), GX-GL11079 (serotype 2) and GX-NN09032 (serotype 5) strains with the low protection rate of 41.7, 58.3 and 58.3%, respectively. The vaccine 4/91 (serotype 5) has provided lower protection rate against the challenge with GX-GL11079 (serotype 2, 75.0%) compared to GX-NN09032 (serotype 5, 83.7%). Interestingly, the vaccine 4/91 (serotype 5) provided the same protection rate (83.7%) against the challenge with isolate GX-YL5 (serotype 1) and GX-NN09032 (serotype 5), but the viral loads of trachea and kidney from GX-NN09032 challenged birds were always lower than those from GX-YL5 challenged birds. Therefore, our data indicated that the vaccine 4/91 had a greater ability to inhibit the replication and reduce the shedding of a homologous serotype virus than a heterologous serotype virus; the vaccine H120 provided poor protection against the heterologous serotype viruses. These findings support the necessity of developing new vaccines whose antigenicity match the antigenic profile of current prevalent IBV variants in the region.