Identification of efficacious vaccines against contemporary North American H7 avian influenza viruses

Authors: Spackman, Erica; Pantin Jackwood, Mary; SITARAS, IOANNIS - Oak Ridge Institute For Science And Education (ORISE); Stephens, Christopher; Suarez, David

Submitted to: Avian Diseases
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/4/2020
Publication Date: 8/1/2021
Citation: Spackman, E., Pantin Jackwood, M.J., Sitaras, I., Stephens, C.B., Suarez, D.L. 2021. Identification of efficacious vaccines against contemporary North American H7 avian influenza viruses. Avian Diseases. 65:113–121. https://doi.org/10.1637/aviandiseases-D-20-00109.
DOI: https://doi.org/10.1637/aviandiseases-D-20-00109

Interpretive Summary: Vaccines are used to protect poultry from the most deadly forms of bird flu. However, influenza can change over time so the vaccines needs to be updated to be adequately effective. Here we tested numerous vaccines to ensure they could be effective against the recent H7 subtype bird flu strains seen in the US. A new vaccine type, non-replicating virus particle, was also tested for its ability to protect chickens, and was successful. Finally, all the vaccines which were tested were characterized to show how closely related their protein coats are; more closely related coats are more likely to provide good protection. Other features of the vaccines, such as ability to induce an antibody response and to grow adequately for vaccine production. Through this study vaccines were identified which are expected to protect against strains of bird flu that are likely to affect North American poultry. This will allow for vaccine production to be accelerated if an outbreak occurs.

Technical Abstract: Five vaccines, including four inactivated, whole-virus water-in-oil adjuvanted vaccines and a commercial non-replicating alphavirus vectored RNA particle (RP) vaccine were evaluated in chickens for their ability to provide protection against challenge with a recent H7 highly pathogenic avian influenza virus (AIV) from the US (A/turkey/IN/1403-1/2016 H7N8). One of the inactivated vaccines and the RP vaccine were prepared with A/turkey/IN/16-01571-6/2016 H7N8 low pathogenic AIV (TK/IN/16), which is identical to the challenge virus, except for the proteolytic cleavage site of the HA protein. The remaining 3 inactivated vaccines were prepared with other North American H7 LPAIV viruses. Hemagglutination inhibition assay was used to evaluate the antigenic relationships among the vaccines and selected recent H7 AIV isolates. All five vaccines provided protection against mortality. The inactivated vaccines reduced virus shedding significantly at 2 and 4 days post challenge compared to sham vaccinated chickens. In contrast, the RP vaccine did not significantly reduce virus shedding. The inactivated vaccine prepared with TK/IN/16 elicited the highest antibody responses, which suggests this is a strong candidate for use as an antigen for North American H7 AIVs. Antigenic distance calculations showed that the four inactivated vaccine strains and other selected recent North American H7 isolates are antigenically close. Although all vaccines provided protection against morbidity and mortality, there were differences among the vaccines in immunogenicity and the differences corresponded to variation in the reduction of virus shed among vaccine groups. Antigenic characterization of recent North American H7 isolates showed that the isolates were antigenically close, which suggests that the vaccines evaluated here would be similar enough to provide protection to other North American H7 AIVs. If future H7 outbreaks in poultry warrant vaccination, the field strain can be rapidly evaluated with these antigens and if related, one of these strains, which have been characterized, may be utilized.