The Efficacy Of Recombinant Baculovirus Trivalent Inactivated Vaccine Against H5 And H7 Avian Influenza In Poultry

Highly pathogenic avian influenza is an important zoonotic infectious disease caused by the H5 or H7 subtype avian influenza virus（AIV）,which can result in significant economic losses in poultry industries and great threat to public health.Vaccination is an effective measure to control highly pathogenic avian influenza.The insect cell-baculovirus production technology is a safe and efficient method for large-scale expression of heterologous proteins and have become a powerful platform for vaccine development.The National Avian Influenza Reference Laboratory cooperated with A biological products company to develop the H5/H7 avian influenza recombinant baculovirus trivalent inactivated vaccine（r BH5-11 strain+r BH5-12 strain+r BH7-2 strain）.In this study,we evaluated its safety,efficacy in commercial poultry of the experimental vaccines to provide a scientific basis for the development and application of the recombinant baculovirus vaccine against H5 and H7 avian influenza.The safety and effectiveness test results showed that SPF chickens immunized with single dose（0.3m L）and high-dose（2.0m L）had no adverse reactions within 28 days after immunization;One dose（0.3 m L）of vaccine could induce mean HI antibody titers ranging from 7.9log2 to 8.5log2 against Re-11,Re-12 and H7-Re2 strains in SPF chickens at 3 weeks post vaccination（p.v.）.After challenged with 100CLD₅₀of the H5N6,H5N1 and H7N9 viruses,respectively,at 3 weeks p.v.,all the vaccinated SPF chickens survived without virus shedding and clinical signs during 14 days observation period,while all the chickens in the control groups died within 5 days post challenge.In the study of the relationship between HI antibody level to different vaccine antigens and protection against the H5 and H7 AIV challenge in laboratory chickens,all the immunized chickens with the HI antibody titer（3log2）to H5 and H7 AIV vaccine strains survived during 14 days observation and part of them shed virus at 5days p.c.after the lethal challenge of H5 and H7 AIV,respectively,and all the immunized chickens with the HI antibody titer（≥4log2）to H5 and H7 AIV vaccine strains were completely protected during 14days observation after the lethal challenge.The HI antibody titers to H5 and H7 AIV vaccine strains induced by the H5/H7 avian influenza recombinant baculovirus trivalent vaccine prepared in this study is similar with that of the commercial H5/H7 avian influenza trivalent vaccine at 3 weeks p.v..The above results indicated that three batches of the experimental vaccine are safe and effective for SPF chickens.In the challenge study against the prevalent H5 and H7 AIV strains,the mean HI antibody titers in the vaccinated SPF chickens were above 7.9log2 at 3 weeks p.v.and all the vaccinated birds obtained100%immune protection（100%survival without any clinical signs and virus shedding）after challenged with 2 H5N6 viruses,2 H5N1 viruses,1 H7N9 virus and 1 H7N2 virus,respectively,during the 14 days observation period,while all the chickens in the control groups died within 5 days post challenge.The results show that immunization of the test vaccine can effectively prevent infection of prevalent strains of H5 and H7 subtypes of avian influenza in SPF chickensIn the test of HI antibody duration of the vaccinated SPF chickens,the mean HI antibody titers to H5 Re-11 strain,Re-12 strain and H7-Re2 strain in the 21-day-old SPF chickens inoculated with single dose（0.3m L）of the vaccine were above 4log2 between 2 weeks p.v.and 22 weeks p.v.after immunization.In the test of the vaccine effectiveness evaluation in commercial layers,the mean HI antibody titers to H5 Re-11 strain,Re-12 strain and H7-Re2 strain were above 6log2 between 3 weeks p.v.and 22 weeks p.v.in the 80-day-old commercial layers inoculated with two doses（0.5m L）of the vaccine at 4-week intervals.After challenged with 100CLD₅₀of the H5N6,H5N1 and H7N9 viruses,respectively,at 3 weeks p.v.and 22 weeks p.v.,all the vaccinated layers survived without any clinical signs and virus shedding during the 14 days observation period,while all the chickens in the control groups died within 5 days p.v.;In the test of the vaccine effectiveness evaluation in commercial ducks,the mean HI antibody titers to H5 Re-11,Re-12 and H7-Re2 strains were all above 5.6log2 between 3weeks p.v.and 20 weeks p.v.in the ducks inoculated with two doses（0.5m L）of the vaccine at 2 weeks old and 6 weeks old.All the vaccinated ducks obtained 100%immune protection after challenged with100DLD₅₀of the H5 and H7 subtype avian influenza viruses for potency test,respectively,at 3 weeks p.v.and 20 weeks p.v..The results of this study indicated that the H5/H7 avian influenza recombinant baculovirus trivalent inactivated vaccine has good safety and efficacy in SPF chickens,commercial layers and commercial ducks.,and provided new ideas and scientific basis for the development of avian influenza vaccine.