The nasal spray version of the flu vaccine did not protect young children against swine flu last winter and might not work again this year, health officials said Thursday.
Preliminary results from three studies found that AstraZeneca's FluMist had little or no effect in children against swine flu. That was the most common bug making people sick last winter.
Because this year's version of FluMist is the same, the Centers for Disease Control and Prevention said it's possible the spray vaccine won't work for swine flu this season, either.
But officials say the spray is still OK to use. Though the flu season is just getting started, early tracking suggests swine flu - the H1N1 strain - won't be a big player this year. Other strains are expected to be the major threat and the vaccine works against those, said Dr. Alicia Fry, a CDC flu vaccine expert.
That's why she's choosing a squirt up the nose for her 7-year-old daughter. And "she'd rather have FluMist than a shot" in the arm, Fry said.
But another flu expert, Vanderbilt University's Dr. William Schaffner, said pediatricians might want to opt for flu shots for their young patients "just to be on the safe side."
Why the nasal spray didn't seem to work last year is a mystery: it has strong track record. The company said inadequate refrigeration of some doses shipped last summer could be an explanation.
Annual flu vaccinations are recommended for all Americans ages 6 months and older. Flu shots are made from killed flu virus. FluMist is made using live but weakened virus, and is only approved for ages 2 to 49. The vaccine's makeup can change from year to year, based on what three or four strains are expected to be circulating.
For years, studies have indicated FluMist is the better choice for young children because it prompts a better immune response in kids who have never been sick with the flu. In June, a federal scientific panel took the unusual step of advising doctors to give FluMist to healthy young kids instead of a shot, if available.
Confidence in that decision was shaken a bit last week during a meeting in Atlanta of the same panel - the Advisory Committee on Immunization Practices - when a CDC official presented the results of the three observational studies. The research was done separately by the CDC, the Air Force and AstraZeneca.
"Everyone was sitting around, scratching their heads" at the puzzling results, said Schaffner, who attended the meeting and helped review the research for the panel.
The panel did not vote to change any of its guidance, but there was a consensus more investigation is needed quickly.
"We are working with the CDC to try and understand why this observation is being seen," said Dr. Chris Ambrose, AstraZeneca's vice president of U.S. medical affairs.
The H1N1 swine flu strain first emerged in 2009 and caused a global pandemic. It had been mostly in the background since then but made a strong showing last year.
Flu vaccine effectiveness tends to vary from year to year and from age group to age group. Last winter, flu vaccine was about 60 percent effective overall, which experts consider to be good. And there was no unusual number of flu-related deaths in children, despite FluMist's apparent lack of effectiveness against swine flu.
The bulk of flu-related hospitalizations and deaths last winter were in people ages 25 to 64. Swine flu has a history of being particularly dangerous in younger adults.
The CDC issued a statement Thursday that detailed the results of the three studies. The AstraZeneca study was the largest, involving more than 1,000 children. It found protection was terrible for children ages 2 through 8 but about normal for older children.
It also found lower effectiveness for doses distributed in August and early September. The H1N1 component is easily ruined if the vaccine is not carefully refrigerated. Company officials are investigating the possibility that late-summer lots were exposed to too much heat somewhere along the line, Ambrose said. Records show the lots were kept at the proper temperature while in the company's possession, he said.
Of children ages 2 to 17 who get flu vaccine, 44 percent get FluMist, according to the drugmaker.
The American Academy of Pediatrics issued a statement Thursday, echoing the CDC's advice that it's important that children be vaccinated - with either a shot or nasal spray.