Evaluation of the protective efficacy of a commercial vaccine against different antigenic groups of H9N2 influenza viruses in chickens.
Despite the long-term vaccination programs implemented in China, H9N2 avian influenza viruses (AIVs) continue to persist in chicken populations, even in vaccinated flocks. We previously demonstrated that H9N2 AIV isolated from chickens in China also underwent antigenic drift and evolved into distinct antigenic groups (C, D and E). To understand whether antigenic drift of viruses away from the vaccine strain partially contributed to the circulation of H9N2 AIV in China, we evaluated the protective efficacy of a commercial vaccine against different antigenic groups of H9N2 AIV. Challenge experiments using vaccinated chickens indicated that the vaccine prevented shedding of antigenic group C viruses, but not those of the more recent groups D and E. Vaccinated chickens, even those with vaccine-induced HI titers of 1:1024, shed virus after being infected with A/chicken/Shandong/ZB/2007, a representative virus of antigenic group D. Genetic analysis showed that the representative viruses of antigenic groups D and E possessed greater numbers of amino acid substitutions in the hemagglutinin protein compared to the vaccine strain and the antigenic group C virus, and many of which were located in antigenic sites. Our results indicated that the persistence of H9N2 AIV in China might be due to incomplete vaccine protection, and that the avian influenza vaccine should be regularly evaluated and updated to maintain optimal protection. Furthermore, the avian influenza vaccination policy also needs to be re-assessed, and increased veterinary biosecurity on farms, rather than vaccine application alone, should be implemented to prevent and control avian influenza.
Key Laboratory of Animal Epidemiology and Zoonosis, Ministry of Agriculture, College of Veterinary Medicine, China Agricultural University, Beijing 100193, China.
Yipeng
Y
Sun
Juan
J
Pu
Lihong
L
Fan
Honglei
H
Sun
Jingjing
J
Wang
Yi
Y
Zhang
Linqing
L
Liu
Jinhua
J
Liu
D000818:Animals; D000956:Antigens, Viral / Q000737:chemistry / Q000276:immunology*; D002645:Chickens; D002681:China; D053127:Influenza A Virus, H9N2 Subtype / Q000276:immunology*; D007252:Influenza Vaccines / Q000276:immunology*; D005585:Influenza in Birds / Q000276:immunology / Q000517:prevention & control / Q000821:virology*
D000956:Antigens, Viral; D007252:Influenza Vaccines