Chilling the Flu Virus

"You get better protection from a live virus vaccine," explains Louise Herlocher, who recently completed a two-year postdoctoral fellowship at St. Jude Children's Research Hospital in Memphis, Tenn. "With a killed vaccine, which can't reproduce in the body and can't infect the host, you get a circulating immune defense. But with the live vaccine, you get a localized response in the nasal passage, which is important because that's where the virus enters the body. For instance, one dose of live vaccine, administered by nose drops, is sufficient to immunize children. So it's always been a goal to develop a live virus that would be safe."

About 30 years ago, Herlocher's mentor at Michigan, John Maassab, took a flu virus that thrived at body temperature and forced it to reproduce at successively lower temperatures. The result was a cold-adapted virus that can't grow in the lungs, but can grow in the much cooler nasal passage, where a localized immune response can destroy invading viral particles.

During the last 20 years, about 15,000 people at six U.S. research hospitals have received this vaccine, and the results have been favorable. "People don't get sick from it, and it doesn't pass to family members," Herlocher says. Most important, when the vaccine is given in conjunction with the killed vaccine in the elderly, it greatly improves their immune response.

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