Evaluation of immune response in calves vaccinated with baculovirus vectored inactivated vaccine expressing 2.3.4.4b H5 protein of highly pathogenic avian influenza virus

Authors: Lee, Chang; GLOVER, SHERRY - Medgene; Olivier, Timothy; Lee, Youngsub; ERICKSON, SARA - Medgene; GUSTAFSON, BRADLEY - Medgene; SHARMA, BISHWAS - Medgene; YOUNG, ALAN - Medgene; SCHUELER, AMBER - Medgene

Submitted to: Veterinary Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/2/2026
Publication Date: 3/3/2026
Citation: Lee, C.W., Glover, S., Olivier, T.L., Lee, Y., Erickson, S., Gustafson, B., Sharma, B., Young, A.J., Schueler, A. 2026. Evaluation of immune response in calves vaccinated with baculovirus vectored inactivated vaccine expressing 2.3.4.4b H5 protein of highly pathogenic avian influenza virus. Veterinary Microbiology. Volume 316. https://doi.org/10.1016/j.vetmic.2026.110970.
DOI: https://doi.org/10.1016/j.vetmic.2026.110970

Interpretive Summary: H5N1 highly pathogenic avian influenza (HPAI) virus is circulating widely in US dairy cattle with significant implications for milk production and cow health. As part of a nationwide effort to develop vaccine against bovine HPAI that is readily applicable in the US, baculovirus vectored inactivated HPAI vaccine was quickly developed using a licensed vaccine production platform. The vaccine was tested in 5-month-old calves and no adverse effect after subcutaneous injection was observed. The vaccine induced detectable antibody response after single vaccination and the level of antibody response increased significantly after a 2nd vaccination. All vaccinated animals showed high antibody titers which was greater than the titer cut-off generally considered to provide protective immunity against HPAI virus challenge. One of the concerns related to vaccination is it could mask an infection in an animal which may negatively affect surveillance effort and be used to justify trade restriction. Our results show that both commercial ELISA and ARS developed assay (N1 NI-ELLA) can be applied as companion DIVA (differentiation of infected from vaccinated animals) surveillance tests. In summary, this study demonstrates that baculovirus vectored H5 vaccine is immunogenic in calves and induces high level of a neutralizing antibody response after two vaccinations.

Technical Abstract: Clade 2.3.4.4b H5N1 highly pathogenic avian influenza (HPAI) virus is circulating widely in US dairy cattle with significant implications for milk production and cow health. Due to the critical need for intervention strategies for continuing outbreaks of bovine HPAI, a baculovirus vectored inactivated HPAI vaccine expressing the 2.3.4.4b H5 protein (Avian Influenza-H5) was quickly developed utilizing a licensed prescription platform which has been tested and proven safe in multiple species. The immunogenicity of recombinant Avian Influenza-H5 vaccine was tested in 5-month-old calves and both the vaccine (n=20 animals) and placebo (n=10 animals) groups showed minor post-injection site swelling that resolved without further affect (or compromise) to the animal after subcutaneous injection of the inoculum. The vaccine induced a measurable immune response by ELISA 3 weeks post-vaccination although the antibody response was low or undetectable by virus neutralization (VN) or hemagglutination inhibition (HI) tests. Two- and four weeks after a 2nd vaccination, antibody titers greater than > 40, which are typically considered minimum protective titer against HPAI virus challenge, were consistently observed in all the vaccinated animals by both HI and VN tests. Strong correlation between VN and HI titers (Pearson correlation coefficient (r) greater than 0.8) were observed. Because the vaccine only contains the H5 protein of influenza virus, all vaccinated animals were negative against nucleoprotein (NP) and N1 neuraminidase antibody by commercial NP ELISA and N1 specific enzyme linked lectin assay, respectively, which confirm the vaccine is DIVA (differentiation of infected from vaccinated) surveillance compatible. In summary, this study demonstrates that an inactivated baculovirus-vectored vaccine, Avian Influenza-H5, is immunogenic and generates presumed protective antibody levels in calves, although future studies evaluating the vaccine in lactating dairy cattle would determine the induction of local immunity in the mammary gland and milk, and if the vaccine provides field protection against influenza-induced mastitis.