Efficacy of commercial recombinant HVT vaccines against a North American clade 2.3.4.4b H5N1 Highly Pathogenic Avian Influenza Virus in chickens

Authors: LEE, JIHO - Orise Fellow; Lee, Chang; Suarez, David; Lee, Scott; Kim, Taejoong; Spackman, Erica

Submitted to: PLOS ONE
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/1/2024
Publication Date: N/A
Citation: N/A

Interpretive Summary: Bird flu is deadly for poultry. Vaccines can preserve the health of the animal and can reduce the spread of the disease. There are many types of vaccines that can be used successfully in poultry. One type, rHVT, uses a benign carrier virus to deliver the protein that induces immunity. These rHVT based vaccines have been used for decades in chickens and are known to be very safe and effective. In this study, two rHVT based vaccines that are licensed in the US were evaluated for how well they worked to protect chickens against the current bird flu strain in the US. Both vaccines provided excellent protection against death and disease in both layer and meat type chickens. The vaccines also reduced how much virus was excreted, so are expected to decrease disease spread too. Finally, because vaccines can eliminate disease, it can be difficult to determine whether a flock has ever been infected with bird flu. Even if chickens are vaccinated it is important to track the virus and to determine if the virus is present in the field. Therefore, a new test that can determine whether vaccinated chickens were ever infected with bird flu was assessed during this study and was successful at identifying healthy birds that were infected with bird flu.

Technical Abstract: The world-wide outbreak of clade 2.3.4.4b H5 highly pathogenic avian influenza (HPAI) in North America that started in 2021 has increased interest in applying vaccination as a strategy to help control and prevent the disease in poultry. Two commercially available vaccines based on the recombinant herpes virus of turkeys (rHVT) vector were tested against a recent North American clade 2.3.4.4b isolate: A/turkey/Indiana/22-003707-003/2022 H5N1 HPAI virus in specific pathogen free white leghorn (WL) (egg layer type) chickens and commercial broiler (meat type) chickens. One rHVT-H5 vaccine encodes a hemagglutinin (HA) gene designed by the computationally optimized broadly reactive antigen (COBRA) method (COBRA-HVT vaccine). The other encodes an HA gene of a clade 2.2 virus, A/mute swan/Hungary/4999/2006 (2.2-HVT vaccine). Except for one broiler, antibody titers to the challenge virus measured 25 days post vaccination by hemagglutinin inhibition (HI) assay were below the detection limit. In contrast, when testing by HI assay using the most similar HA antigen to each vaccine that was available, 63.3% and 100% of the chickens were positive in the COBRA-HVT and 2.2-HVT vaccinated groups, respectively. Morbidity, mortality, and viral shedding among all vaccinated groups were compared with sham vaccinated controls. There was 100% survival of both WL and broilers in the COBRA-HVT vaccinated groups and in the clade 2.2-HVT vaccinated groups there was 94.8% and 90% survival of the WL and broilers respectively. Compared to the 2.2-HVT vaccinated groups, WL in the COBRA-HVT vaccinated group shed significantly lower mean viral titers by the cloacal route and broilers shed significantly lower titers than the WL by the oropharyngeal route. Virus titers detected in oral and cloacal swabs were otherwise similar among both vaccine groups and chicken breeds. To assess antibody-based tests to identify birds that have been infected after vaccination (DIVA-VI), sera collected at 7-, 10-, and 14-days post challenge (DPC) were tested with enzyme-linked lectin assay-neuraminidase inhibition (ELLA-NI) for N1 neuraminidase antibody detection and by commercial ELISA for detection of antibodies to the NP protein. As early as 7DPC 100% of the chickens were positive for N1 antibody by ELLA-NI. ELISA was less sensitive with a maximum of 75% positive at 10DPC in broilers vaccinated with 2.2-HVT. Both vaccines provided protection from challenge with a current HPAI virus to both breeds of chickens and ELLA-NI was sensitive at identifying antibodies to the challenge virus therefore should be evaluated further for DIVA-VI.