A nasal spray appears to be more effective than flu shots in protecting children under 5, according to a major new study.

Researchers gave either flu shots or MedImmune's FluMist nasal spray to almost 8,000 young children in 2004 and found that of the nearly 500 children who caught the flu, those given shots caught it twice as often.

The study, published in the New England Journal of Medicine, was funded by MedImmune, which is trying to persuade the Food and Drug Administration to approve FluMist for use by children between ages 1 and 5. Researchers at the St. Louis University medical school say it's the largest pediatric study conducted comparing flu shots to the spray.

"It's good news. We need it, we need a new flu vaccine for children," said Neal A. Halsey, director of the Institute for Vaccine Safety at the Johns Hopkins Bloomberg School of Public Health. He was not involved in the study.

Robert B. Belshe, the lead investigator and a professor of medicine and pediatrics at St. Louis University School of Medicine, said the spray works better in children because it's a weakened version of live flu virus. Injected vaccine is killed virus.

"The live vaccine gives a broader response, better than a flu shot," Belshe said.

Another advantage, he said, is that while shots stimulate antibodies in the blood, the nasal spray stimulates antibodies in the blood and the nose.

"Shots are good at boosting pre-existing immunity," he said. "But they don't work as well where there is no pre-existing immunity."

The FDA approved FluMist for people between 5 and 49 in June 2003 but withheld approval for children under 5 because of previous studies linking it to wheezing problems among some youngsters. A refrigerated version of FluMist was approved by the FDA in January and is due to replace the current frozen formula, which has been criticized for having difficult storage requirements.

The study shows FluMist is safe for children from 1 to 5 with no history of wheezing or asthma, said Belshe. But, he said, there is still a need for a safe vaccine for children under a year old. The study results show that 42 of the infants between 6 to 11 months old were hospitalized within six months of being given the nasal spray, compared with 18 hospitalization cases among infants given shots.

Belshe called the hospitalization rates "puzzling" and said many of the hospitalized children had problems largely unrelated to flu, such as diarrhea and lung infections.

In an accompanying editorial, the New England Journal of Medicine editors called the results encouraging, but they recommend "further discussion and careful review" of safety data before FluMist is approved for young children.

"They're simply calling for caution and that's appropriate," Belshe said. "We're talking about a very vulnerable population."

In the study, 7,852 children aged 6 months to 59 months received either the nasal spray or a flu shot at 249 hospitals and health-care facilities in 16 countries. Those given active doses of the spray also were given placebo shots; those given real shots got a placebo spray. Influenza-like symptoms were then monitored and nasal swab cultures were taken throughout the 2004-2005 flu season.

Of the 491 children infected during the ensuing flu season, 338 had been given flu shots and 153 had received nasal spray, which translates into 54.9 percent fewer flu cases. The spray was particularly effective at preventing the most common of the three strains of flu that cause illness each year, reducing cases of the H3N2 strain of flu virus by 79 percent.

"The efficacy was significant," Halsey said.