Avian influenza virus could kill millions.

• Position: Pandemics

A harmless virus used as a delivery vehicle may help set a roadblock for a potentially catastrophic outbreak of bird flu in humans, assert researchers at Purdue University, West Lafayette, Ind., and the Centers for Disease Control and Prevention, Atlanta.

Purdue molecular virologist Suresh Mittal and his collaborators are investigating a new way to provide immunity against avian influenza viruses, or bird flu, the most lethal of which, H5N1, has a 50% fatality rate in humans.

The researchers are focusing on using a harmless virus, called adenovirus, as a transmitting agent for a vaccine to fight off highly virulent strains of the avian influenza viruses. Current vaccines are designed for strains of flu found in local areas and are effective only as long as the virus does not change form. Existing vaccines will have limited success against new strains of avian influenza. Every time a bird flu mutates, vaccines must be redesigned.

Another advantage to using an adenovirus as a vector, or transporter of vaccine into cells, is that it could be mass produced much more quickly than with current models. "Our approach is to use an adenovirus to deliver some components of the bird flu virus in a vaccine formulation," Mittal explains. "We already know how to grow large amounts of adenovirus and how to purify it because adenoviruses already are used in clinical trials for gene therapy as vectors. The ultimate goal of our research is to develop an effective avian influenza virus vaccine that will provide long-lasting and broad immunity against multiple strains of this virus."

The proteins that form the basis for all of today's flu vaccines are grown in fertilized chicken eggs. It takes months to produce a vaccine for a new virus strain using this method and limits supplies due to shortages in eggs for that purpose. The egg production method also creates difficulty in redesigning the vaccine to keep pace with virus mutations.

"Do we still want to depend on the egg to make our flu vaccines?" Mittal wonders. "When these types of viruses strike humans, they also strike poultry. In that case, the availability of fertilized eggs to make enough vaccine will be compromised."

A "medium-level" bird flu pandemic in the U.S. would kill between 90200,000 people with another 20-47,000,000 sickened, CDC experts estimate. The economic impact alone would be between $71-166,500,000,000. Influenza viruses are respiratory pathogens responsible for widespread infections in...