Even as the federal Centers for Disease Control and Prevention tightened the reins on the supply of flu vaccine late last year, it recommended for the first time that children between 6 months and 2 years old get the shot. The rationale: Children are often hospitalized with the flu, and they also can infect other people quite easily. But does the flu vaccine really keep kids from getting sick? European researchers surveyed studies of the effectiveness of vaccinating children.

What the researchers wanted to know: Does vaccinating children for the flu work?

What they did: The researchers collected and examined published studies, searching medical journals and contacting vaccine manufacturers about unpublished research. The researchers were looking for a consensus about whether vaccination prevented the flu and reduced the incidence of illness, hospitalization, and school absences.

What they found: For children younger than age 2, the flu vaccine did no better than a sugar pill, or placebo, at protecting them from the flu. Vaccination did protect about 70 percent of children ages 2 to 16 from getting the flu but didn't do much to reduce the rate of other flulike illnesses, sick days, or hospitalizations. The researchers' best guess was that among children who got sick, a noninfluenza virus had often made them ill. A live-attenuated virus (often given in the United States nasally in the FluMist vaccine) was more effective at preventing flu than the inactivated vaccine, which usually is given as a shot. (In the United States, the FluMist vaccine is approved only for people between the ages of 5 and 49.)

What it means to you: Standing in line for hours to get your children vaccinated may not be worth it. If your child is under 2, there is little evidence that vaccination will help. The vaccine seems to work better at protecting older children, though it doesn't appear to reduce sick days, flulike illness, or hospitalizations. On the other hand, there is very little risk, and your child could be one of those who benefits. See what your child's pediatrician thinks.

Caveats: While the researchers found strong, similar results across multiple studies, many of the studies were difficult to compare because of different follow-up periods or interventions. The researchers cautioned that their conclusions cannot be considered absolute.

Find out more: U.S. News has reported on all aspects of flu vaccination, including the question of kids' safety. For more, go to our website for an archive of stories.

The CDC website offers information about flu, including specific information about preventing and treating the flu in children.

Read the article: Jefferson, T. et al. "Assessment of the Efficacy and Effectiveness of Influenza Vaccines in Healthy Children: Systematic Review." The Lancet. Feb. 26, 2005, Vol. 365, No. 9461, pp. 773–780.

Abstract online: www.thelancet.com (registration required)