Sanofi pasteur, the vaccines unit of Sanofi-Aventis, said Thursday that preliminary results of a clinical trial in France show that its bird flu vaccine candidate showed a good immune response in volunteers.

After inoculating 300 healthy volunteers with a vaccine candidate for H5N1, the bird flu strain of most concern, immune responses were "at levels consistent with requirements of regulatory agencies for licensure of seasonal influenza vaccine" in a significant number of volunteers, the company said in a statement.

The vaccine candidate included an additional ingredient, or adjuvant, to increase the effectiveness of the treatment.

The company will release more data as it becomes available and plans to use the study to assemble a dossier for European regulators to reduce the necessary time for an approval during a flu pandemic.

The World Health Organization estimates that the next flu pandemic could result in 1 million to 2.3 million hospitalizations and 280,000 to 650,000 deaths in industrialized nations alone, with significantly higher casualties in developing countries.