Efficacy of inactivated and RNA particle vaccines against a North American Clade 2.3.4.4b H5 highly pathogenic avian influenza virus in chickens.

• Four vaccines were tested for efficacy against clade 2.3.4.4b in chickens. • All four vaccines protected against morbidity and mortality. • All four vaccines reduced virus shed compared to sham vaccinates. • Antibodies to the challenge virus could be detected at 7 days post challenge. • These licensed vaccines are efficacious for current epornitic H5 avian influenza. Highly pathogenic avian influenza virus (HPAIV) has caused widespread outbreaks in poultry in the Americas. Because of the duration and extent of these outbreaks, vaccine use may be an additional tool to limit virus spread. Three vaccines were evaluated for efficacy in chickens against a current North American clade 2.3.4.4b H5 HPAIV isolate, A/turkey/Indiana/3703-003/2022 H5N1. The vaccines included: 1) a commercial inactivated reverse genetics (rg) generated H5N1 product with a clade 2.3.4.4c H5 hemagglutinin (HA) (rgH5N1); 2) a commercial alphavirus RNA particle (RP) vaccine with the TK/IN/22 HA; and 3) an in-house inactivated rg produced vaccine with the TK/IN/22 HA and a North American lineage N9 neuraminidase (NA) (SEP-22-N9). Both inactivated vaccines were produced with HA genes that were modified to be low pathogenic and with the remaining genes from the PR8 influenza strain. All vaccines provided 100% protection against mortality and morbidity and all vaccines reduced virus shed by the oropharyngeal and cloacal routes significantly compared to sham vaccinates. However, differences were observed among the vaccines in quantities of virus shed at two- and four-days post challenge (DPC). To determine if infected birds could be identified after vaccination to aid surveillance programs, serum was collected from the RP and SEP-22-N9 vaccine groups at 7, 10, and 14 DPC to detect antibody to the NA and nucleoprotein (NP) of the challenge virus by enzyme linked lectin assay (ELLA) and ELISA. As early as 7DPC ELLA detected antibody in sera from 100% of the chickens in the RP vaccinated group and 70% of the chickens in the SEP-22-N9 vaccinated group. Antibody to the NP was detected by commercial ELISA in more than 50% of the birds in the RP vaccinated group at each time point. [ABSTRACT FROM AUTHOR]