| Highly pathogenic avian influenza(HPAI)is a lethal infectious disease caused by H5 and H7 subtypes of influenza A virus,which resulted in serious harm to the poultry industry,and posed great threat to public health.Vaccination is one of the important strategies of prevention and control of avian influenza in China.On account of the high mutation rate of avian influenza virus in nature,vaccine should be regularly evaluated and vaccine strains should be updated if necessary.The surveillance,virus analysis and evaluation of the protection efficacy evaluation were carried out by National Avian Influenza Reference laboratory.The results showed that the H7N9 viruses isolated in poultry in 2019 showed distinct antigenicity to H7N9 H7-Re2 vaccine strain which was used for trivalent vaccine production,and partial protection against the challenge of the epidemic virus was observed and the vaccine seed needs to be updated.The H5 subtype viruses isolated recently showed similar antigenicity to the H5 vaccine seed(Re-11 and Re-12 strains),and the vaccine prepared with H5N1 Re-11,Re-12 and H7-Re2 stains can provide full protection against the H5 virus challenge,so the H5 vaccine strains could be used for vaccine development.To control the H7N9 antigenic variants in poultry,the ressortant H7N9 vaccine seed candidate was generated by using reverse genetics by National Avian Influenza Reference laboratory,and designed as H7-Re3 strain.In this study,we firstly evaluated the biological characteristics,passage stability and immunogenicity of H7-Re3 strain,and found that the H7-Re3 strain could be propagated stably in chicken embryos with high growth properties,showed nonpathogenic to chicken embryos and chickens,exhibited good immunogenicity with effective prevention against the challenge of H7N9 virus in chickens,and thereby could be an ideal inactivated avian influenza vaccine strain.Subsequently,H5 subtype Re-11 strain,Re-12 strain and H7 subtype H7-Re3 strain were inoculated in chicken embryos,respectively,and the allantoic fluid of the infected chicken embryoses were harvested for three-time concentration,inactivation by formalin,and further emulsion.Three batches of trivalent inactivated avian influenza vaccines were prepared in this study.The vaccine character,safety,immune efficacy had been tested in this study.The immune protection against epidemic strains and the relationship between HI antibody response and protection in H5 and H7 HPAI were also evaluated in this study.The results showed that the three batches of vaccines meet the vaccine quality criterion;there were no adverse reactions in poultry immunized with a high dose of 2ml of the vaccine per bird.After inoculation with the recommended dose(0.3ml),the HI antibody average titers to H5 subtype Re-11 strain,Re-12 strain and H7 subtype H7-Re3 strain in SPF chickens were above7.7log2.The HI antibody titers were between 1:124 and 1:148 at 3 weeks in SPF ducks immunized with one dose(0.5ml)of the vaccine,and the HI antibody titers to the three vaccine strains were between 1:32and 1:44 in commercial geese at 3 weeks post immunization;After 3 weeks,the immunized birds were challenge with the H5 subtype clade 2.3.4.4d,clade 2.3.2.1d viruses and H7N9 antigenic variants for potency test,and the vaccinated birds were challenged with the prevalent strains.The results showed that the immunized poultry survived without any clinical signs,and virus shedding were not observed in the vaccinated group after challenge with different lethal viruses,respectively,which indicated that three batches of H5+H7 trivalent inactivated vaccine could provide complete immune protection against the challenge of H7N9 antigenic variant strains detected in poultry in 2019,H5 subtype clade 2.3.4.4d and 2.3.2.1d viruses.The research on the relationship between HI antibody response and protection of the vaccine showed that the immunized chickens could be complete protected against the challenge of H5 and H7 subtype strain when HI antibody titers(?4log2)to Re-11 strain,Re-12 strain and H7 subtype H7-Re3 strain were detected in the vaccinated chickens,and immunized duck could be protected against of the challenge with homologous H5 subtype and heterologous H7 subtype avian influenza viruses When the HI antibodies HI antibody titers(?1:10)to Re-11 strain,Re-12 strain and H7 subtype H7-Re3 strain were detected in the vaccinated ducks.Furthermore,we evaluated the application of the recombinant avian influenza virus(H5+H7)trivalent inactivated vaccine prepared by Re-11,Re-12,and H7-Re3 vaccine seeds in field poultry,mainly including its safety and immune efficacy.A white feather broiler breeder farm in Shandong,a commercial layer hen farm in Harbin,a layer breeder farm in Ningxia,and a breed duck farm in Shandong were selected for vaccine field test.The results showed that there was no adverse reaction in the vaccinated field poultry,and the high-level HI antibody titers were induced in chickens and ducks immunized with the vaccine according to the vaccination procedure,which indicated the good immunity in commercial chickens and ducks for the control of the H5 and H7 subtypes of highly pathogenic avian influenza.This study showed that the recombinant avian influenza virus(H5+H7)trivalent inactivated vaccine based on Re-11,Re-12,and H7-Re3 vaccine seeds showed good safety and immune efficacy in chickens and waterfowl.The vaccine has been authorized for its application in China since July 2020 and has played a very important role in the prevention and control of H5 and H7 avian influenza. |
PDF Full Text Request