However, no significant increase in risk was seen after the second or third dose.

In a five-year of Rotarix, researchers from the U.S. Centers for Disease Control and Prevention (CDC) looked at 207,955 doses, including 115,908 first doses and 92,047 second doses, and identified 5.3 extra cases of intussusception within seven days after the administration of either dose. Only 0.72 cases would be expected per 100,000 unvaccinated young children.

In an accompanying editorial, Roger Glass of the National Institutes of Health and Umesh Parashar of the CDC wrote that the results of the studies should be interpreted with caution.

"What, then, is the message for the physician or nurse who administers rotavirus vaccines, and what is the implication for vaccine policy in developed countries?" the two asked.

"Certainly, the abundance of evidence in the United States and beyond indicates that intussusception can occur as a result of vaccination with either RV5 or RV1, but the risk is low, on the order of approximately 1 to 5 cases per 100,000 infants, with wide confidence limits."

"Many questions remain to be resolved ... (however,) the public health benefits of rotavirus vaccines ... are likely to be substantial and outweigh a small risk of intussusception," they added.