BOSTON -- Flu season is lurking just around the corner, and those at risk -- such as children under 2 and the elderly -- are already eligible to get their shots.

New data compiled by researchers at Harvard and Children's Hospital found that neither of those groups is the first to get the flu and spread it, reported WCVB-TV in Boston. Research indicates that preschoolers are bringing the flu home first.

"Three- and 4-year-olds are, in fact, the early spreaders of influenza," said Dr. John Brownstein, of Harvard University.

The AEGIS computer system compiled data from five different health care settings in Boston from 2000 to 2004. During that time, 3- and 4-year-olds were treated for the flu three to four weeks before any other age groups, as early as late September.

Children under age 2 began arriving a week or two later, while older children first arrived in October and adults began arriving only in November.

The findings are published in the Oct. 1 issue of the American Journal of Epidemiology.

"We believe that they are not only early, but they are important in the spread as well," said Dr. Kenneth Mandl, of Children's Hospital Boston.

The researchers said child-care centers and preschools with many children in close quarters are hotbeds of infection.

"They're getting sick in the school setting and coming home and spread to their parents and grandparents, and they're getting sick and potentially dying," Brownstein said.

So why aren't those children getting the first flu shots?

Three- and 4-year-olds generally can overcome the flu, which means they are not in the at-risk groups that receive their flu shots early in the season -- even though they may be the ones spreading the virus.

"What the study suggests is the interesting possibility that you could also look to vaccinate age groups or other target populations who are not necessarily vulnerable themselves, but are important in spreading it to the vulnerable," said Mandl.

But Dr. Robert Lindeman of Natick Pediatrics said that's not realistic, given the less-than-adequate supply of flu vaccine.

"If there were enough influenza vaccine to go around, the entire United States population should be vaccinated in my view. But there isn't enough vaccine to go around," he said.

The study's authors agreed that if the flu vaccine is in short supply, it must go to the vulnerable first. But, they said, this new information will help to predict the severity of the upcoming flu season and find new strategies for controlling the flu in 3- and 4-year-olds.

• Study Abstract