Due to the spread of the H5N1 highly pathogenic strain of avian influenza virus across Europe, a preventive vaccination occurred in early 2006 among 135 French zoologic institutions. Approximately 25,000 birds were vaccinated with a H5N2 inactivated vaccine. Among them, 4,369 birds were monitored by members of Association Francophone des Vétérinaires de Parc Zoologique regarding safety issues of the vaccination protocol. A total of 1,686 blood samples were collected before the first injection (n = 255), at the time of booster (n = 463), 60 day after the booster (n = 514), and 180 day (n = 229) and 330 day (n = 217) after the initial injection. Thus, sera of 126 species representing 15 different avian orders were tested using the hemagglutinin inhibition assay to evaluate seroconversion and the long-term serologic profile of selected anti-H5 antibody. Safety was considered satisfactory in all orders, and there were no deleterious effects on large-volume injection/body weight ratio. After the second injection, 71% of the birds developed a titer ≥32, with a mean titer of 558. Titers then decreased in all birds, with 42% of the remaining birds having a titer ≥32 at day 180 and only 26% at day 330. Results demonstrated that a booster 42 days after initial vaccination was mandatory to raise the titer above 32, considered to be the protective level in poultry, and to increase the number of seroconverted birds. Differences in the serologic responses among the orders and species of birds were detected and could be linked with the variation of vaccine dose injected per body weight or with species-specific immune response. The protocol for additional campaigns will be adjusted for some bird orders through the increase of injected dose or a half yearly booster to sustain better titers over the year. Vaccination is a useful tool, together with biosecurity, that should always be used as a primary method of preventing and controlling avian influenza outbreaks.
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Vol. 40 • No. 4