Baxter to Launch Trial of Pandemic Flu Vaccine

Baxter International announced it plans to initiate a Phase III trial of its investigational adjuvant-free pandemic H5N1 influenza vaccine to confirm the results of a Phase I/II study.

The Phase I/II study indicated that Baxter's candidate vaccine is highly immunogenic at low doses and induces substantial levels of cross immunity against widely divergent H5N1 strains. The open-label, multicenter, Phase III trial is designed to evaluate the safety and efficacy of Baxter's adjuvant-free, whole-virus avian flu vaccine. Vaccinations will begin in the first half of this year, and results are scheduled to be available by the end of 2007.

Baxter's candidate H5N1 vaccine is derived from H5N1 strain A/Vietnam/1203/2004. Its antigen composition and structure closely resemble the actual pathogen circulating in nature. The candidate vaccine induces an immune response that is similar to the body's defense against a natural virus, without the need to incorporate additional agents to enhance immune response. It is manufactured using the company's proprietary vero cell technology, which produces high-yield vaccine more quickly than traditional approaches because it is not produced in eggs. Baxter's candidate vaccine is the first cell-based candidate H5N1 pandemic vaccine to undergo clinical evaluation.

The Phase I/II trial tested four different antigen concentrations: 3.75 to 30 micrograms with adjuvant and 7.5- and 15-microgram formulations with and without adjuvant. In the 7.5-microgram formulation without adjuvant, the seroprotection rate at day 42 was 76.2 percent. Immunity induced by the vaccine also neutralized divergent H5N1 virus strains such as the Clade 3 strain A/Hong Kong/156/97 and the Clade 2 strain A/Indonesia/05/05, Baxter said.

In the Phase III trial, volunteers will be administered vaccine without adjuvant. Recipients will be evaluated for the vaccine's ability to elicit the production of antibodies to the H5N1 strain A/Vietnam/1203/2004 and a number of divergent strains.