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Babies vaccinated against rotavirus, the leading cause of severe diarrhea in infants and young children worldwide, may have a small risk of a dangerous intestinal blockage, researchers reported Tuesday.

But researchers for the Centers for Disease Control and Prevention (CDC) say the risk is very small and vaccination is still worthwhile. Vaccination “is still very beneficial,” said Dr. Frank DeStefano, director of the CDC’s Immunization Safety Office, who worked on one of the two studies published in the New England Journal of Medicine.

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Before vaccination was introduced in the U.S. in 2006, rotavirus sent about 200,000 children to the emergency room, put 55,000 to 70,000 in the hospital, and killed 20 to 60 children under 5 years old each year. Vaccination has made a dramatic difference, averting 65,000 hospitalizations from 2007 to 2009, according to CDC estimates.

Two rotavirus vaccines are licensed in the U.S., RotaTeq since 2006 and Rotarix since 2008. In 1999, another vaccine, RotaShield, was voluntarily withdrawn a year after it hit the market because of an association with intussusception, the “telescoping” of one segment of intestine inside another. The blockage that results can tear the intestines.

In a five-year study of Rotarix, DeStefano’s team found 5.3 extra cases of intussusception per 100,000 vaccinated infants. Less than one case would be expected per 100,000 unvaccinated infants.

In a seven-year study of RotaTeq, another group of researchers found 1.5 extra cases of intussusception per 100,000 vaccinated infants. Again, less than one case would be expected per 100,000 unvaccinated infants.

“I would call this a relatively small risk,” said Dr. Katherine Yih, a researcher at the Harvard Pilgrim Health Care Institute, who led the RotaTeq research. “It’s about one-tenth the additional risk of the original vaccine that was recalled in 1999.”

Tuesday’s studies, along with others in Australia, Brazil and Mexico, “taken together, indicate that there is a small increased risk of intussusception with both vaccines, but the benefits of either vaccine outweigh the risks associated with vaccination,” said DeStefano.

The CDC’s Advisory Committee on Immunization Practices agrees and continues to recommend rotavirus vaccination.