MONDAY, Oct. 6, 2008 (HealthDay News) -- Over the past two flu seasons, vaccinating children five and younger did not reduce the number of child hospitalizations or doctor's visits linked to influenza, according to results of a new study.
Given the poor match between the flu vaccine and circulating strains during the last two years, "this finding is not surprising," said Dr. Robert Belshe, a professor of medicine and pediatrics and director of the Center for Vaccine Development at the Saint Louis University Medical Center, who was not involved in the study.
"We know that the inactivated vaccine -- the flu shot -- doesn't work real well in children, particularly when the virus has evolved and drifted away from the type that is put in the vaccine," he said.
In contrast, the live attenuated vaccine given as a nasal spray is far more effective, Belshe contended. "A recent study showed that it is 50 percent more effective at protecting against flu, including these drifted viruses that don't match," he said.
Another study, this time in the October issue of Pediatrics, found that deaths caused by flu-linked staph infection are climbing among U.S. children, so the flu shot may still be important.
In June 2006, the Centers for Disease Control and Prevention (CDC) recommended for the first time that all children 6 months of age or older receive annual flu shots.
The new report was published in the October issue of the Archives of Pediatrics & Adolescent Medicine.
In the study, a team led by Dr. Peter G. Szilagyi, from the University of Rochester School of Medicine and Dentistry and Strong Memorial Hospital in Rochester, N.Y., looked at 414 children aged five and younger who developed flu in the 2003-2004 or 2004-2005 flu seasons.
Among these children, 245 were seen in hospitals or emergency departments, and 169 were cared for in a doctor's office or clinic. The researchers compared the vaccination status of these children with more than 5,000 children from the same area who did not get the flu.
Szilagyi's group found that children who got the flu were less likely to have been vaccinated, compared with children who didn't get sick.
However, after they adjusted for flu risk factors -- such as a child's location, sex, insurance status, chronic health conditions or timing of the vaccine -- the effectiveness of the vaccine could no longer be shown. The effectiveness of the flu shot ranged from 7 percent to 52 percent for 6- to 59-month-old children who had been fully vaccinated, the researchers found.
The less-than-perfect match between the strain of flu in the vaccine during the two seasons studied and the flu that was actually circulating may have contributed substantially to the poor effectiveness of the vaccine, Szilagyi's team speculated.
In 2003 to 2004, 99 percent of circulating flu was influenza A, but only 11 percent of the influenza A strain in the United States was similar to the strains included in the vaccine.
"The 2004-2005 season was less severe, and the vaccine was a better match to circulating strains than in 2003-2004, but still only 36 percent of virus isolates were antigenically similar to vaccine strains," the authors noted.
From September 2007 to April 2008, the CDC reported a total of 72 deaths from flu among children with many more hospitalized.
Belshe said that, for children over two, the nasal flu vaccine should be used instead of an injection. "It is recommended for children and adults, aged 2 to 49 who do not have asthma or recurrent wheezing -- that's about 80 percent of children," he said.
For younger children, "you're stuck with a flu shot -- no pun intended," Belshe said. "The flu shots should still be used. It probably modifies the severity of the illness, even though it doesn't protect completely against the illness itself -- it is important to take," he said.
Dr. William Schaffner, department chairman of the division of infectious disease and professor of preventive medicine at Vanderbilt University, noted that to be fully protected, young children need two doses of flu vaccine, which many don't get.
"Adults have had much more experience with both influenza and influenza vaccine," Schaffner added. "The likelihood that the vaccine is going to give you a boost in immunity is stronger in adults than it is in children," he said.
Schaffner noted that over the past 20 years, the match between the vaccine and the circulating flu virus has generally been good.
"In about four-fifths of the time, the experts have been pretty much on target, including the appropriate material in the vaccine. Occasionally, because the flu is fickle, it outfoxes those of us who select what's going to be in the vaccine," Schaffner said.
As for the coming flu season, the CDC in September announced that it was "optimistic" that the vaccine created this time around will be a closer match to circulating viruses.
"It's not a great vaccine, [but] it's a good vaccine. The best tool we have is the influenza vaccine -- recognizing that every once in a while, getting your influenza vaccine is not going to give you perfect protection," he said.
And any protection may be vital, according to the study in Pediatrics. In that work, researchers at the CDC analyzed data on pediatric flu deaths from the 2004-2005 season through to the 2006-2007 season.
They found that the number of kids who died of the flu over the three seasons rose from 47 and 46 in the first two years, to 73 in the 2006-2007 season. Many of the deaths were attributed to tough-to-treat staph infections. More than half of the children who died were between 5 and 17 years of age and had previously been healthy, the team noted.
The overall risk to an individual child is still very low, "but it's an important message to say even healthy children develop complications and die almost before anything much can be done for them," one vaccine specialist, the Mayo Clinic's Dr. Gregory Poland, told the Associated Press.
Schaffner stressed that vaccination is still important, but he agreed with Belshe that the nasal spray vaccine is better for children.
"The nasal spray vaccine provides broader protection against influenza virus variants than does the injectable vaccine," Schaffner said. "There are many of us who would like to see more children vaccinated and more nasal spray vaccine used. Any vaccine is better than none. Nasal spray vaccine should be used more frequently."
For more about flu, visit the Centers for Disease Control and Prevention.