Two experimental vaccines for rotavirus, a common cause of diarrhea in children, prevent serious disease and show no signs of causing the rare but dangerous side effect that derailed an earlier rotavirus vaccine, say reports from two of the largest vaccine safety trials ever done.
The studies published in today's
New England Journal of Medicine, each of which involved more than 60,000 babies, show that Merck's RotaTeq and GlaxoSmithKline's Rotarix "demonstrate an impressive efficacy profile," write Roger Glass and Umesh Parashar of the Centers for Disease Control and Prevention in an editorial.
"Perhaps even more important," they write, is that the vaccines show a "reassuring safety profile, particularly with respect to intussusception," the sometimes fatal bowel obstruction associated with Wyeth's RotaShield. The vaccine was pulled from the market in 1999, less than a year after it was licensed in the USA.
In the studies, RotaTeq prevented 98% of severe rotavirus illnesses and Rotarix prevented 85%, a difference that could be attributed to variations in the criteria for "severe disease" or to the populations studied, the editorial says.
Rotavirus is the leading cause of diarrhea illness in toddlers. It afflicts virtually all children by age 5 but takes its highest toll in developing countries, where it is responsible for more than 500,000 child deaths a year from dehydration. In the USA, rotavirus deaths are rare, but infections send about 70,000 children to the hospital each year.
Intussusception, a telescoping of the intestinal walls, occurs in about 1 of every 2,000 babies in the first year of life. The first rotavirus vaccine increased the risk 20 to 30 times within two weeks of the first dose, the CDC says. Studies to test the safety of the new vaccines needed to be large enough so that any association with intussusception would be apparent, said Penny Heaton, Merck's senior director for vaccine clinical research.
Both vaccines are to be given by mouth, but there are differences between the two. The Glaxo vaccine contains the most common strain of rotavirus and is given in two doses, a month or two apart; the Merck vaccine contains five strains and is given in three doses, at 2, 4 and 6 months old.
Glaxo's vaccine has been approved for use in Mexico and 14 Latin American countries and is expected to be available in Europe later this year. The company has not yet sought U.S. Food and Drug Administration approval.
Merck's vaccine has been under FDA review and was recommended for approval last month by an advisory panel. If the agency grants a license within the next few weeks, the vaccine could be added to the routine list of childhood immunizations when the CDC's Advisory Committee on Immunization Practices meets in February.
It's not certain whether the vaccines will be as effective in the poorest countries, where children are exposed to a variety of health problems that can affect their ability to respond to some vaccines, says John Wecker, director of the Rotavirus Vaccine Program at PATH (formerly the Program for Appropriate Technology and Health), a non-profit international health agency. To find out, Glaxo has begun clinical testing in South Africa, Malawi and Bangladesh; Merck is planning trials in Africa and Asia later this year.
"There's a clear need for an effective way to prevent rotavirus disease in the developing world," Wecker said. The new vaccines "have tremendous potential, but they've been tested primarily in the U.S., Europe and Latin America. The key question is to determine whether these vaccines work equally well in the poorest children of the world."
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