Bug versus bug: insect virus makes a viable flu vaccine.

A new influenza vaccine churned out by caterpillar cells prevents the flu, researchers say. The advance might eventually revolutionize the manufacture of flu vaccine, now produced in chicken eggs in a long, cumbersome process prone to contamination and other failures.

After successful safety tests, "this is the first time this ... vaccine has been shown to protect people against the flu," says John J. Treanor of the University of Rochester (N.Y.) Medical Center, who led the study reported in the April 11 Journal of the American Medical Association.

During the 2004-2005 flu season, none of 151 recipients of a high dose of the new vaccine caught the bug. Two of 150 people receiving a low dose came down with the flu, while 7 of 153 people receiving a sham vaccine got sick.

The study "absolutely showed protection," says Doris Bucher of New York Medical College in Valhalla, whose lab grows the seed strains of influenza virus for conventional vaccines.

The new vaccine is produced by caterpillar cells infected with a genetically modified baculovirus. In its normal form, this virus prolifically produces a protein called polyhedron, which coats and protects the virus particles as they rest on leaves before being eaten by a caterpillar.

The vaccine developers replaced the polyhedron gene with the gene for hemagglutinin, an influenza protein. Lab-grown insect cells infected with the modified baculovirus then churned out large amounts of hemagglutinin, which elicited flu-fighting antibodies when injected into people, according to the new findings.

Each strain of influenza carries a slightly different hemagglutinin gene, and each year public health officials make an educated guess as to which strains will emerge around the globe. Vaccine makers then target the predicted strains. If the officials guess wrong, as they did in 2003, the vaccine produced offers little protection.

But with the new method, says Treanor, the appropriate hemagglutinin gene could be quickly inserted into baculovirus, speeding production of effective vaccines.

Each year, influenza kills some 36,000 people in the United States and hospitalizes another 226,000, according to the Centers for Disease Control and Prevention in Atlanta. Three manufacturers annually produce 100 million doses of flu vaccine for the United States in a process that takes 6 months from identification of emerging strains in Asia to putting vaccine in vials.

Daniel Adams, president and chief executive officer of Protein Sciences Corporation of Meriden, Conn., which developed the new vaccine and funded the study, says that the company's process could cut production time to 2 months.

Such an acceleration could save lives. Treanor says, "We know that even a few weeks of saved time ... can make a big difference."

However, Bucher cautions that researchers haven't yet demonstrated large-scale vaccine production from insect cells.

Gary Nabel, director of the Vaccine Research Center at the National Institutes of Health in Bethesda, Md., agrees. "Overall, I'd say it's encouraging. [But] is it ready to swoop in tomorrow and replace conventional vaccines? No."