Squirts for squirts: flu spray guards kids.

A squirt up the nose could provide a shot in the arm for the flu vaccination program. A new study reveals that a nasal spray vaccine prevents influenza in healthy children, who are 2 to 10 times more likely to get the disease than adults and who often spread the virus to others.

Only 1 percent of 1,070 children treated with the nasal vaccine developed flu last winter, compared to 18 percent of the 532 children who received a spray with no active ingredient, announced the National Institute of Allergy and Infectious Diseases (NIAID) in Bethesda, Md., and Aviron, a pharmaceutical company in Mountain View, Calif., this week.

"This is a new public health tool with which to control influenza," says research team member Robert B. Belshe of Saint Louis University School of Medicine. "if we vaccinate at school, we might eliminate the major mechanism of transmission in the community."

Although the currently licensed injectable flu vaccine works for healthy children, public health strategists have traditionally targeted people who are at highest risk of complications from influenza--those over 65 and those with one of several chronic diseases. Aviron plans to make the nasal vaccine available for widespread use in 1999, pending approval by the Food and Drug Administration.

Scientists don't know how effective the nasal vaccine alone is in the elderly, but results from a 1992 study at the University of Rochester (N.Y.) indicate that a combination of the two vaccines improves protection in this population, says Dominick A. Iacuzio, influenza program officer at NIAID.

The new study employs a virus that reproduces in the relatively cool nasal passages but not in the warmer environment of the lungs. As a result, the vaccine strain induces immunity but not disease. Scientists have been refining such cold-adapted flu viruses for over 30 years, since they were first isolated by Hunein F. Maassab at the University of Michigan School of Public Health in Ann Arbor.

Like the injectable version, the nasal vaccine stimulates antibody production in the blood. In addition, it signals cells in the mucous lining of the upper airway to manufacture a kind of antibody that they alone can make. Both antibody types may be important in preventing flu, says Belshe. "This should confer a more complete immune response than the currently used vaccine."

Influenza virus disguises itself with a new coat every year. Consequently, scientists need a way to make a vaccine that's effective against each emerging strain.

For the nasal vaccine, they mix the emerging virus with a master strain that grows at temperatures so low the wild virus can't reproduce. When the two strains are cultivated together, new viruses--with some properties of each--occasionally arise. Scientists then grow the old and new viruses at low temperatures, thus disabling the wild strain, and inactivate the master strain by using compounds that bind to its surface. This leaves a virus that reproduces only under cool conditions and has the emerging strain's coat.

While the new study is "first-rate," says epidemiologist Raymond A. Strikas of the Centers for Disease Control and Prevention in Atlanta, it would be expensive to vaccinate millions of children, and the health and economic benefits won't be clear until more studies are conducted. He also points out that the investigators did not compare the nasal and injected vaccines.

"The real benefit is that we're likely to get more people to take it," Iacuzio says.

Sandy Prichard, the St. Louis mother of two young participants in the study, agrees. "I didn't dread bringing them to the doctor like I do when they're going to get a shot," she says.