Abstract

In 2003 highly pathogenic avian influenza virus (H7N7) struck poultry in the Netherlands. A European Commission directive made vaccination of valuable species in zoo collections possible under strict conditions. We determined pre- and post-vaccination antibody titres in 211 birds by hemagglutination inhibition test as a measure of vaccine efficacy. After booster vaccination with an inactivated H7N1 vaccine, 81.5% of vaccinated zoo birds developed a titre of ≥40, while overall geometric mean titre (GMT) was 190 (95% CI: range=144–251). GMT and percentages with a titre ≥40 were related to taxonomic order. Birds of the orders Anseriformes, Galliformes and Phoenicopteriformes showed higher GMT and a larger percentage of these birds developed titres ≥40 than birds in other orders. There was an inverse correlation between published average weight per species and antibody response.¹

In December 2005, when HPAI H5N1 infected birds were found in several countries in the Near East and the virus was thought to spread into Europe, zoo birds were vaccinated against H5, and residual antibody titres to H7 vaccination were determined in 95 birds.

Approximately 2.5 years after vaccination, 24.2% of the vaccinated birds were still seropositive, although only 12.6% had a titre ≥40. In Anseriformes, Galliformes and Ciconiiformes, titres persisted for longer than in the other taxonomic orders.

In conclusion, the results indicate that the vaccination against H7, although initially effective, would not be protective in most birds 2.5 years post vaccination.

Acknowledgments

We thank the zoos and people involved in collecting the serum samples, and Theo Bestebroer and Chantal Baas for technical laboratory assistance.

Literature Cited

1.  Joost, D.W. Philippa, V.J. Munster, H. van Bolhuis, T.M. Bestebroer, W. Schaftenaar, W.E.P. Beyer, R.A.M. Fouchier, T. Kuiken, and A. Osterhaus. Highly pathogenic avian influenza (H7N7): vaccination of zoo birds and transmission to non-poultry species. Vaccine. 2005;23:5743–5750.