| H5 and H7 highly pathegenecity avian influenza viruses not only cause significant losses to the poultry industry,but also pose a serious threat to human life and health.Vaccination is the key link and the last line of defense against avian influenza and the recombinant avian influenza virus(H5/H7)bivalent inactivated vaccine had been broadly used in 2017 order to fight against H5 and H7 avian influenza viruses.However,according to the results of the national epidemiological investigation of avian influenza,clade 2.3.2.1 and 2.3.4.4 have been the dominant H5 avian influenza viruses since the end of 2017,meanwhile,clade 2.3.4.4d and 2.3.2.1d have become the main epidemic strains threatening the poultry industry in China.Further research showed that the antigenicity was different between Re-8strain and representative strains of clade 2.3.4.4 D and 2.3.2.1 separated in 2018,and the bivalent inactivated vaccine could not offer complete protection against these viruses.Meanwhile,the antigenicity of the H7N9 H7-Re1 strain was quite different from that of H7N9 viruses isolated currently,so that Re-8 and H7N9 H7-Re1 strains needed to be updated simultaneously.In this study,the H5 Re-11,Re-12 and H7-Re2 seed strains were tested firstly,including viral titers,HA and NA gene sequences,toxicity to eggs and chicks,specificity and so on.Then we cultured them until E13,testing the viral titers of all generations.The results showed that Re-11,Re-12 and H7-Re2 seed strains were suitable for chicken embryo proliferation,with high biosafety,strong specificity and good immunogenicity,which means that Re-11,Re-12 and H7-Re2 strains are ideal vaccine seeds.Secondly,the H5/H7 trivalent inactivated vaccine prepared based on Re-11,Re-12 and H7-Re2 seed strains was determined in laboratory studies.The results indicated that the trivalent inactivated vaccine was safe for SPF chickens,SPF ducks and commercial geese,and after post to vaccination21 days,the average HI antibody titers reached above 7.7log2,7.7log2 and 4.2log2,respectively.All the vaccinated chickens were healthy without virus shedding and death after challenge by three highly pathogenic parental strains and the epidemic strains.When the HI antibody titers of H5 and H7 reached3log2,the vaccinated SPF chickens obtained anti-death protection,and complete protection would be got when the HI antibody level reached 4log2 or above.When the Re-11 and Re-12 HI antibody titers reached 2log2,SPF ducks got complete protection against H5 avian influenza viruses,and when the H7-Re2 HI antibody titers was above 3log2,they had complete protection against heterologous H7N2 avian influenza viruses.Finally,we analyzed the safety and HI antibody titers of layers,white broilers,Beijing fatty chichens,,Gushi chickens,commercial white broilers and ducks vaccinated with the trivalent inactivated vaccine,in order to evaluate the clinical application of the vaccine.The results showed that the vaccine was safe enough,meanwhile,it could induce high antibody titers in layers,white broilers,Beijing fatty chichens,Gushi chickens,and ducks.Commercial white broilers immunized with trivalent inactivated vaccine could obtain high HI antibody titers before slaughter.The recombinant avian influenza virus(H5/H7)trivalent inactivated vaccine has great safety and immunogenicity target to chickens and waterfowls.This vaccine has been used broadly in China since2019 and plays an important role in avian influenza control and precaution. |
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