Serum reactivity analysis with inactivated GVII-matched vaccine-Payavax G79®: Comparison of B-cell epitopes in NDV-vaccine strains.

The Newcastle Disease Virus (NDV) sub-genotype VII.1.1 is the most common NDV circulating in Iranian poultry farms. It differs genetically and antigenically from the conventional vaccine strains of genotypes I and II. The inactivated vaccines efficiency can be affected by the grade of similarity with circulating viruses. Here, we updated the NDV vaccine using a local circulating virus seed, introduced Payavax G79® as the inactivated bivalent vaccine, and compared the results with serological and phylogenetic characteristics derived from it to different NDV genotype virus vaccines. According to our results, after 25 days post-vaccination, the antibody titer elicited against sub-genotype VII.1.1 was 8.4 log2. In contrast, the antibody titer against apathogenic genotype I (NDV-V4) and lentogenic genotype II (LaSota) was 4.4 log2 and 4 log2, respectively. Comparing in silico studies of the F protein's discontinued B-cell epitopes, it was found that NDV-GVII, LaSota, and NDV-V4 virus all have seven, four, and eight discontinued B-cell epitopes on the protein's surface. Furthermore, the HN protein surface of NDV-GVII, LaSota, and NDV-V4 virus has four, six, and three discontinued B-cell epitopes, respectively. In summary, the low similarity between NDV genotypes I, II, and the predominant circulating genotype VII (approximately 83-84 %) indicates the need for an updated vaccine seed strain.