Injection no better than a placebo at preventing influenza in children

Jan 25 2006

U.S. health authorities should have waited for more evidence before recommending routine flu shots for healthy toddlers, according to a new systematic review of studies involving half a million children worldwide.

Only a few studies of the vaccine have been conducted in children under 2 years old, and findings suggest that the injection is no better than a placebo at preventing influenza. Moreover, only one tiny study has looked specifically at the safety of flu shots in toddlers.

Based on these findings, the reviewers question whether all healthy children between 6 months and 23 months of age should receive the flu shot as recommended by the U.S. Centers for Disease Control and Prevention since 2004.

“National policies for the vaccination of healthy young children are based on very little evidence,” say the authors, led by Dr. Sue Smith of Oxford University.

The review appears in the current issue of The Cochrane Library, a publication of The Cochrane Collaboration, an international organization that evaluates medical research. Systematic reviews draw evidence-based conclusions about medical practice after considering both the content and quality of existing medical trials on a topic.

Until recently, flu shots were promoted primarily for those with chronic illnesses, people over age 65 and health-care workers. However, studies have shown that children under 2 are hospitalized for flu at the same rate as senior citizens, and the CDC reported that more than 150 children under 18 died from complications of flu during the 2003-2004 season.

The Cochrane review comprised 51 studies of influenza vaccines - including 17 papers translated from Russian for the first time - involving more than 250,000 healthy youngsters under age 16.

Yet only a fraction of these studies focused on children younger than 2. Two efficacy studies involving about 1,000 toddlers indicate that flu shots containing inactivated virus - the only vaccine approved for this age group - are no more effective at preventing the flu than placebo.

Furthermore, the reviewers “found no evidence to back up the claims that the vaccines prevent deaths from influenza or other serious complications,” said coauthor Dr. Tom Jefferson of the Cochrane Collaboration vaccine program. “They may do so, but there is no evidence at present.”

Nearly three dozen studies on vaccine safety followed a similar pattern. “We were astonished to find only one safety study of inactivated vaccine in children under 2 years carried out nearly 30 years ago in 35 children,” say the review authors.

Although 11 studies presented safety data for flu shots in youngsters up to 18 years old, such aggregate data is inadequate for assessing safety among toddlers, said Jefferson.

For children older than 2, the findings are quite different. More than 15,000 observations from high-quality studies indicate that flu shots prevent influenza in 59 percent of children who receive them. A nasal spray vaccine made from live virus - approved since 2004 for children over 5 - is even better, with 79 percent efficacy.

Safety data for older children were collected and reported in such a wide variety of formats that no analysis was possible. “There is an immediate need to standardize safety outcome data,” says the review.

Given the paucity of research on children under 2, the review also calls for more randomized trials on the efficacy and safety of inactivated vaccine in this age group. “All this homework should be done before the vaccine is recommended for use in any population, not after,” said Jefferson.

Yet devoting too much time to research also has downsides, said Henry Bernstein, M.D., a Dartmouth Medical School pediatrician and member of the American Academy of Pediatrics Committee on Infectious Diseases.

“It would be a shame to wait until every study from A to Z is completed before recommending vaccination,” he said. After all, children would be dying from the flu in the meantime.

“It’s a difference in strategy. We know the vaccine is safe and effective in older people, the chronically ill and health-care workers. There’s no reason to believe the same thing wouldn’t help in 6- to 23-month olds.” Monitoring of vaccine responses continues long after they are in widespread use to catch any rare problems that may appear, he added.

Only half of the 180 million Americans who should receive flu vaccine are currently protected, says Bernstein. “Large research projects are expensive. I’d rather spend the money on education and making the vaccine available to all who need it.”