Key Laboratory of Animal Epidemiology and Zoonosis, Ministry of Agriculture, College of Veterinary Medicine, China Agricultural University, Beijing 100193, China.
Vet Microbiol. 2012 Apr 23;156(1-2):193-9. doi: 10.1016/j.vetmic.2011.10.003. Epub 2011 Oct 10.
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.
尽管中国实施了长期的疫苗接种计划，但 H9N2 禽流感病毒（AIV）仍在鸡群中持续存在，即使是在接种过疫苗的禽类中。我们之前已经证明，从中国鸡群中分离出的 H9N2 AIV 也发生了抗原漂移，并进化成了不同的抗原群（C、D 和 E）。为了了解病毒的抗原漂移是否部分导致了 H9N2 AIV 在我国的传播，我们评估了一种商业疫苗对不同抗原群 H9N2 AIV 的保护效果。用接种疫苗的鸡进行的攻毒实验表明，该疫苗可以预防抗原群 C 病毒的脱落，但不能预防最近出现的抗原群 D 和 E 病毒的脱落。接种疫苗的鸡，即使其 HI 滴度达到 1:1024，在感染了抗原群 D 的代表病毒 A/chicken/Shandong/ZB/2007 后仍会脱落病毒。遗传分析表明，抗原群 D 和 E 的代表病毒在血凝素蛋白上具有比疫苗株和抗原群 C 病毒更多的氨基酸替换，其中许多位于抗原位点。我们的结果表明，H9N2 AIV 在我国的持续存在可能是由于疫苗保护不完全，因此需要定期评估和更新禽流感疫苗，以保持最佳保护效果。此外，还需要重新评估禽流感疫苗接种政策，并在农场实施更严格的兽医生物安全措施，而不仅仅是疫苗接种，以预防和控制禽流感。
