Chiron Corporation's preliminary data from a clinical study of its investigational vaccine against an H9N2 avian influenza strain that has infected a small number of people and may have the potential to cause a human pandemic is promising. The trial was supported by the National Institute of Allergy and Infectious Diseases (NIAID), part of the US National Institutes of Health (NIH).

According to a company release the 96-patient study explored the safety and immunogenicity of four different doses of the investigational vaccine with and without Chiron's adjuvant MF59. An adjuvant is a substance that is added to a vaccine to boost the body's immune response to the vaccine's antigen.

All vaccine formulations containing the adjuvant MF59 proved highly immunogenic, inducing antibody levels believed to confer protection against the influenza strain. The lowest dose contained 3.75 micrograms of antigen per dose, a quarter of the dose used in seasonal influenza vaccines. In marked contrast, the unadjuvanted vaccine induced significantly lower antibody titers and did not reach levels achieved by the adjuvanted vaccine following any of the antigen doses tested, which ranged from 3.75 to 30 micrograms.

"This study builds on the clinical data Chiron has already established with adjuvanted influenza vaccines. With more than 20 million doses of MF59-adjuvanted vaccine distributed outside of the United States for seasonal vaccination, we have built an impressive safety database. In addition, our previous clinical studies of a vaccine designed to protect against H5 avian influenza have demonstrated the potential of our adjuvant to reduce the required dose of antigen and to cross-protect against a range of related viral strains," said Rino Rappuoli, chief scientific officer of Chiron and head of research for Chiron Vaccines.

"This important collaborative research further advances our understanding of the role innovative adjuvant technology can play in enhancing the immune response to pandemic vaccines, providing the potential for dose-sparing to stretch production capacity. Following these successful results, we look forward to clinical studies of an adjuvanted H5N1 vaccine planned for the near future," continued Dr. Rappuoli

Pandemic influenza occurs when a new influenza virus emerges that is easily transmitted among humans and causes serious illness. In this situation, the virus can result in a worldwide outbreak of disease, or pandemic. Pandemic influenza occurred three times in the last century. The 1918 pandemic killed at least 40 million people worldwide, with a mortality rate of approximately 2.5 percent in the United States.