Safety and Immunogenicity of Poultry Vaccine for Protecting Critically Endangered Avian Species against Highly Pathogenic Avian Influenza Virus, United States

Abstract

In 2023, an outbreak of highly pathogenic avian influenza occurred among critically endangered California condors (Gymnogyps californianus), and >21 died. We evaluated safety, immunogenicity, vaccination strategies, and correlates of antibody response of an influenza vaccine for poultry in black vultures (Coragyps atratus) and then California condors. We noted differences in antibody titers between vaccinated and unvaccinated birds (vultures p<0.004; condors p-<0.02) but no adverse effects of vaccination. All vaccinated vultures and 80% of vaccinated condors showed maximum measured antibody response within the published range associated with survival of vaccinated and virally challenged chickens. We noted weak evidence of higher antibody responses for birds given two 0.5-mL vaccines versus those given one 1-mL vaccine but no correlation between antibody titers and sex for either species or between antibody titers and bone lead concentrations in vultures. Our results prompted initiation of a vaccination program for condors that could reduce spread of this disease among highly threatened species.

Keywords: Black vulture; California condor; Coragyps atratus; Gymnogyps californianus; H5N1; Influenza; United States; highly pathogenic avian influenza virus; inactivated vaccine; respiratory infections; viruses; zoonoses.

Figure 1

Photographs of avian species tested in study of safety and immunogenicity of poultry vaccine for protecting critically endangered avian species from highly pathogenic avian influenza virus, United States. A) California condor (Gymnogyps californianus), whose infection with highly pathogenic avian influenza virus was the motivation for this research. B) Black vulture (Coragryps atratus), closely related species used as a surrogate for condors in this research. Photo credits: panel A, US Fish and Wildlife Service public domain; panel B, Todd E. Katzner.

Figure 2

Hemagglutination inhibition (HI) titers in a study of safety and immunogenicity of poultry vaccine for protecting critically endangered avian species from highly pathogenic avian influenza virus, United States. A) Titers for 28 black vultures (Coragryps atratus); B) titers for 25 California condors (Gymnogyps californianus). Birds were included in 1 of 3 highly pathogenic avian influenza vaccine trial groups comprised of 10 birds given two 0.5-mL vaccinations at days 0 and 21, another 10 birds given a single 1-mL vaccination at day 0, and 8 vultures and 5 condors that were unvaccinated negative controls. Vaccinated animals were given a 1057.R1 serial 590088 avian influenza vaccine, H5N1 subtype, reverse genetics-derived, inactivated vaccine (see main text for details on the vaccine). For vultures, postvaccination blood draws were conducted at 10, 21, 31, and 42 days after first vaccination; for condors, blood draws were on days 21 and 42. Box tops and bottoms show quartiles, whiskers are 95% CI, dots outliers; X indicates 0 values for control groups.