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How Your Vaccines are Approved

Vaccine approval process questioned after rotovirus recall.

WebMD Feature

The immunization rate for children is at an all-time high of 80%, according to the Centers for Disease Control and Prevention (CDC). But in light of the recent withdrawal from the market of a vaccine against rotavirus, should parents be more leery of the process by which vaccines are approved?

"My daughter was constipated for months after she received the rotavirus vaccine at the age of 2 months," says Amy Blackmon of Port Saint Lucy, Fla. "When I heard that there were bad reactions to a vaccine that my doctor had recommended, it made me think I should know more about other immunization shots my daughter is getting."

Rotavirus infection causes diarrhea, vomiting, and mild fever. Nearly all children have at least one bout by the age of three. The American Academy of Pediatrics reports that each year up to 50,000 children and adults are hospitalized because of the virus, and that 20 to 40 people die from it.

Why the Vaccine Was Approved -- Then Withdrawn

The rotavirus vaccine was approved by the U.S. Food and Drug Administration in fall 1998. But by the following July the CDC was recommending that the vaccine not be used -- based on a rise in the number of cases of a type of bowel obstruction called intussusception among children who had received the vaccine.

A low rate of intussusception was noted in the pre-licensing tests for the vaccine, "so the FDA requested ongoing tests after licensing," says Barbara Reynolds, spokeswoman for the CDC. "As soon as the vaccine was being used on larger numbers, the higher rate of occurrence of the problem was detected very quickly."

After only one year on the market, the vaccine was withdrawn by its manufacturer, Wyeth Ayerst Laboratories, last October. "That the rotavirus vaccine was withdrawn shows the safety net the system provides is working," maintains Reynolds.

"It is almost never possible to do pre-licensing studies that are large enough to find very rare events with great certainty," says Robert Lowell Davis, M.D., a professor of pediatrics at the University of Washington and a vaccine safety researcher at the Group Health Cooperative, Immunization Studies Program. "We have to find the correct balance between safety and making new preventive tools -- such as vaccines -- at a cost our society can afford."

According to David O. Matson, M.D. -- Associate Director of the Virginia Medical School's Center for Pediatric Research -- intussusception occurs at a rate of about 50 per 100,000 children who are vaccinated with the rotavirus vaccine in the first year of life -- an extremely low rate. A study to detect potentially dangerous events at such a low rate would require more than 50,000 participants, and would cost the vaccine manufacturer about $2,000 per participant.

Matson notes that the rotavirus vaccine is the first vaccine recommended for routine use in children that has ever been withdrawn.

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