A better flu shot.

Getting a flu shot hurts, but getting the flu is even worse. Every winter, sore throats, fevers, and other flu symptoms keep lots of kids home from school. And unfortunately, the shot, which is supposed to prevent people from getting the flu, doesn't always work as well as doctors would like.

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Now, researches have found a new, quicker way to make flu vaccines that might work better. Their secret weapon? Caterpillar cells.

In a study during the 2004-2005 flu season, 151 people were given a high dose of a caterpillar-assisted vaccine. None came down with the flu. Just 2 of 150 people who got a low dose of the new vaccine got sick. In comparison, 7 of 153 people given a fake vaccine developed the flu.

"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.

The flu, also called influenza, is caused by a virus that mutates over time. So, every summer, scientists try to guess which strains of the virus are going to spread around the globe the next winter. They then develop a vaccine to fight those strains.

The old vaccine contains a small amount of the influenza virus. Given the right dose, our bodies learn how to fight the virus without actually getting sick.

For years, vaccine makers have grown the old flu vaccine inside of chicken eggs. Doing this, however, takes 6 months. That's too long to make changes during years when the vaccine isn't working as well as it should.

That's why some researchers think that caterpillar cells might make better flu-vaccine factories than chicken eggs. In the study, researchers at Protein Sciences Corporation grew caterpillar cells in the lab. Then, they infected the cells with a type of insect virus called a baculovirus.

Normally, baculovirus produces a specific baculovirus protein. The researchers altered the virus, however, so that it churned out an influenza protein instead. When injected into people, this protein caused their immune systems to build up defenses against the flu.

Each strain of influenza makes a slightly different version of the influenza protein. Using caterpillar cells as factories instead of chicken eggs, scientists could make quicker changes if they realized that the vaccine they were currently making would not be effective against the coming flu season's strain.

The new technique would take 2 months instead of 6 to produce flu vaccines, the researchers say. That speed could save lives. About 36,000 people die of the flu in the United States each year. Another 226,000 end up in the hospital because of it.

But before caterpillar cells can become a front-line weapon against the flu, scientists have some more work to do.

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