A new version of the nasal spray vaccine FluMist is better at preventing influenza than traditional flu shots in older babies and children, according to a study sponsored by its maker, MedImmune.

The spray also dramatically reduced the risk of flu-related ear and lower respiratory tract infections, said the report published on Wednesday in the New England Journal of Medicine.

But for infants age 6 to 12 months, or older children who sometimes wheeze when they breathe, old-fashioned shots are safer, the researchers found.

Results of the worldwide test on 8,400 preschoolers, conducted during the 2004-2005 flu season, are being released as health officials encourage flu vaccinations for those aged 6 months to 5 years to prevent the spread of the virus.

But old-fashioned shots, which use killed virus particles, provide less protection to children under 5 than to adults, and may cause more side effects. The spray uses live weakened viruses.

Robert Belshe of the Saint Louis University School of Medicine in Missouri and colleagues found both treatments reduced children’s flu rate, but half as many of those who got nasal spray became ill as those who received flu shots.

While 8.6 percent of children getting injections developed flu, the rate was 3.9 percent for kids given the spray.

Regular influenza kills an average of 36,000 Americans every year, and up to 500,000 people globally. While most victims are elderly, more than 100 U.S. children, many of them previously healthy, can die in an average flu season.
Succeeding by a nose

FluMist is squirted up the nose using a special device.

“The big difference is the induction of antibodies in the nose, which is important because this is where the flu virus usually enters the body. The nasal spray flu vaccine appears to induce a more complete immune response,” Belshe said.

The study used a new version of FluMist that does not need to be kept frozen, only refrigerated. U.S. regulators approved it last month for healthy children and adults age 5 to 49.

Researchers also discovered the spray worked against strains that had mutated slightly over time drift.

“That translates into very high protection even when the circulating strains don’t precisely match the vaccine strains,” Belshe said in a telephone interview.

But the spray vaccine may carry special risks for recipients younger than 1. Those babies were more likely to develop wheezing and 2.3 times more likely to be hospitalized for any cause if they received FluMist instead of the shots.

Youngsters who had a history of wheezing before receiving the shots were excluded from the test.

So for children less than one year old or older children with a history of wheezing, “the flu shot remains the vaccine of choice because of the safety issues,” Belshe said.

“For children over 12 months of age who do not have a history of wheezing, and that’s approximately 80 percent of children, it looks like the intranasal vaccine is the better choice,” he said.

MedImmune hopes to expand its market by showing that the spray, first licensed in the United States in 2003, is safe and effective for preschoolers, who are particularly vulnerable to flu. A decision from the U.S. Food and Drug Administration is expected by the end of May.