CVI Accepts, published online ahead of print on 3 October 2007

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Clin. Vaccine Immunol. doi:10.1128/CVI.00174-07
Copyright (c) 2007, American Society for Microbiology and/or the Listed Authors/Institutions. All Rights Reserved.

Development and evaluation of an influenza subtype H7N2 vaccine candidate for pandemic preparedness

Claudia Pappas, Yumiko Matsuoka, David E. Swayne, and Ruben O. Donis^*

Influenza Division, Centers for Disease Control and Prevention, Atlanta, GA and Southeast Poultry Research Laboratory, Agricultural Research Service, United States Department of Agriculture, Athens, GA

^* To whom correspondence should be addressed. Email: rdonis{at}cdc.gov.

Influenza virus of the H7N2 subtype has been introduced into non-commercial poultry in the United States and probably resulted in incidents of transmission of H7N2 virus to humans, documented in 2002 and 2003. This virus could be considered a potential threat to public health if it acquired person-to-person transmissibility. A favored approach for global pandemic preparedness includes development of pre-pandemic vaccines for any potential pandemic virus. To this end, we created a high growth reassortant virus (H7N2-PR8) containing the genes for the hemagglutinin (HA) and the neuraminidase (NA) from a low pathogenic (H7N2) virus strain and the remaining six genes from a human vaccine strain (H1N1). The reassortant strain was evaluated to assess its antigenicity, safety and protective efficacy using a mouse model. Antigenicity studies using ferret antibodies raised against H7N2-PR8 indicated that this virus confers broad cross-reactivity with divergent H7 viruses of different years and lineages. Mice and chickens inoculated with high doses of H7N2-PR8 supported virus replication but survived, indicating that this virus is comparable to other avian viruses of low pathogenicity. To assess the protective efficacy of H7N2-PR8, mice were immunized with two doses of formalin-inactivated A/H7N2-PR8, alone or with alum. Vaccinated mice subsequently challenged with highly pathogenic viruses from homologous and heterologous lineages, A/Canada/444/04 (H7N3) and A/Netherlands/219/03 (H7N7), revealed pronounced reduction of wild type virus replication. These studies indicate that, A/H7N2-PR8 is immunogenic, safe and protective in animal models; these are the essential attributes to qualify for Phase I human clinical trials as a pre-pandemic vaccine.

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