Comparative testing of vaccines based on viruses of genetic lineages G1 and Y280 for their potency against low pathogenic avian influenza H9N2

Abstract

Due to the genetic diversity of low pathogenic avian influenza (LPAI) viruses of subtype H9N2, it deemed appropriate to study the potency of the vaccines based on the antigens of strains А/chicken/Amursky/03/12 and A/chicken/Chelyabinsk/314-1/20 that represent currently circulating in the Russian Federation genetic lineages Y280 and G1, respectively. While low pathogenicity of the agent does not allow demonstrating the vaccine protective properties by the direct methods generally used for potency assessment (e.g. morbidity and mortality), the indirect methods were used: determination of antigenic relatedness of the strains, level of the postvaccinal homologous and heterologous humoral immunity, analysis of the virus genome synthesis inhibition (reduction) in vaccinated birds following their challenge. The strains used in the vaccines were determined to have some antigenic differences, which were demonstrated in the hemagglutination inhibition (HI) assay during control of the postvaccinal immunity in birds. Both vaccines generally induced strong humoral immunity in vaccinated birds (9–10 log2 determined using HI assay) with some difference in the levels of the immune response following the use of homologous or heterologous antigens. It was also reliably determined that homologous immunity facilitated more expressed inhibition of the virus reproduction after the challenge. The level of inhibition (reduction) of the virulent LPAI virus genome synthesis in vaccinated birds following their challenge with H9N2 virus of genetic lineage G1 was higher in birds following homologous vaccination, while the time periods of the genome detection in the biomaterial samples were the same. It was demonstrated that due to antigenic and immunogenic differences between LPAI H9N2 strains, use of both antigenic components in the inactivated vaccines is appropriate.