Baxter International Inc. announced results from a preliminary evaluation of its phase I/II clinical trial of whole-virus H5N1 influenza candidate vaccine. The results represent the first clinical evaluation of a Vero cell-based candidate H5N1 pandemic vaccine.

The candidate H5N1 pandemic vaccine was produced using the company's proprietary Vero cell-based technology platform and inactivated wild-type H5N1 strain A/Vietnam/1203/2004. The clinical trial was conducted in 270 healthy adults in Austria and Singapore using four different antigen concentrations ranging from 3.75µg to 30µg in formulations. The 7.5µg and 15µg antigen concentrations were tested with and without adjuvant, a substance added to vaccines to improve immune response.

"We are extremely pleased with the clinical results from this study," said Noel Barrett, Ph.D., vice president of Global R&D for Baxter's vaccines business. "We have achieved an important step toward our goal of producing a safe and efficacious pandemic vaccine using the company's proprietary Vero cell-based technology."

Hartmut Ehrlich, M.D., vice president of Global R&D for Baxter BioScience added: "This is the first clinical demonstration that a candidate H5N1 vaccine can induce antibodies that neutralize widely divergent strains of H5N1. These preliminary data, which must be confirmed in a larger study, suggest that the vaccine may provide wider protection for a larger number of people before and during a pandemic."

Preliminary results from this trial suggest that the vaccine is well tolerated in humans: the occurrence and severity of side effects at all dose levels are similar to what has been reported for licensed interpandemic (or seasonal) influenza vaccines. Most common side effects are injection site reactions, headaches and fatigue.

In addition, the preliminary results suggest that the vaccine is highly immunogenic and elicits functional antibodies to H5N1 even at the lowest dose level of 3.75µg. Importantly, preliminary analysis of serum samples obtained from the study subjects suggests both the neutralization of the pandemic virus contained in the vaccine and cross-neutralization against widely diverse strains of H5N1, including both Hongkong/156/97 and Indonesia/05/05.

"These preliminary results are encouraging," said Professor Frank von Sonnenburg, M.D., who heads the Section of International Medicine and Public Health within the Department of Infectious Diseases and Tropical Medicine at the University of Munich, and chairs the Data Safety and Monitoring Board for the clinical study. "If confirmed in Phase III results, the suggested safety and immunogenicity of this cell-culture derived whole virus vaccine indicate its potential to make a major contribution to public health in preparing for and combating an influenza pandemic situation."

Baxter plans to present the initial results of the Phase I/II clinical trial October 11 at the World Vaccine Congress in Lyon, France, and October 20 during the Second International Conference on "Influenza Vaccines for the World" in Vienna, Austria, with final results available by the end of 2006.

The company also plans to begin a Phase III clinical trial of the candidate pandemic vaccine early next year and present final results by the end of 2007.