BACKGROUND: Intussusception was found to be a side effect of the first rotavirus vaccine available in the United States, which was recommended for use in October 1998. As a result, that vaccine was voluntarily withdrawn from the market by the manufacturer in October 1999. That vaccine was estimated to cause intussusception in 1 infant out of every 10,000 infants who received it.

For the two new, next generation rotavirus vaccines available in the United States, the FDA evaluated safety data from large pre-approval studies that were specifically designed and conducted to see if either new vaccine increased the risk of intussusception. In each of these pre-approval studies, about 30,000–35,000 infants were given rotavirus vaccines. Both new vaccines were approved by FDA because these studies showed them to be safe and effective, and these studies did not show an increase in the risk of intussusception. However, even large safety studies may not always be able to detect events that happen rarely.

As with all vaccines, FDA and CDC committed to ongoing safety monitoring of the new rotavirus vaccines after they were approved for use. The manufacturers of both vaccines also committed to conduct postmarketing safety studies (the postmarketing phase is the time after a vaccine is approved and is in use). These ongoing studies gather more and more information as the vaccines are being used, and so it is possible to determine if the vaccines have a risk of intussusception that may have been too low to detect in the studies conducted before vaccine approval.

CURRENTLY: Rotarix vaccine has been available in the United States since 2008. About 2.7 million doses have been distributed. There are not enough safety data from ongoing studies in the United States to allow detection of a level of risk as low as the one found in the Mexico study. The manufacturer, as well as CDC and FDA, are monitoring the safety of this vaccine in the United States.

A safety monitoring study in Mexico conducted by the manufacturer beginning in 2008 shows that Rotarix vaccine may cause intussusception. If the risk for U.S. infants is similar to that found in the Mexico study, it would translate to 0 to 4 cases of intussusception from vaccine per 100,000 U.S. infants who receive the first dose of Rotarix. This risk estimate is much lower than the risk from the earlier rotavirus vaccine, which is no longer available.

Risk of intussusception following rotavirus vaccination: This new information suggests that the risk of intussusception from Rotarix vaccine is low:

• 0 to 4 U.S. infants out of 100,000 infants who receive the first dose of the vaccine.

Intussusception is a rare condition that happens among infants and children, and most of the time the cause is not known. When no rotavirus vaccine was used in the United States, each year about 1,900 infants developed intussusception before the age of 1 year. With rotavirus vaccination, if every U.S. infant received the first dose at the recommended age, and that caused intussusception in 0 to 4 infants out of 100,000 infants, this would mean 0 to 125 more cases of intussusception per year.

Risk of severe rotavirus disease in unvaccinated children: Rotavirus vaccines offer tremendous benefits by protecting infants and children from rotavirus disease. Rotavirus is the most common cause of severe diarrhea among infants and young children.

Before use of rotavirus vaccines, almost every U.S. child became infected with rotavirus before 5 years of age. U.S. children faced significant risks from rotavirus disease:

• 1 child out of every 70 children was hospitalized
• 1 child out of every 17 children went to a hospital emergency department

In the United States before rotavirus vaccination was available, an estimated 20 to 60 children died because of rotavirus disease each year.

Infants and children with rotavirus disease usually suffer watery diarrhea for 3 to 8 days, and vomiting and fever are common. Young children may lose interest in eating and drinking and become dehydrated because they do not take in enough fluids. In severe cases, children need to go to the hospital to receive fluids given directly into a vein using an intravenous line (IV).

BACKGROUND: Among infants born in early 2008, 60% received a full series of rotavirus vaccine. This is about how many would be expected within 2 years after a vaccine is introduced. About 90% of U.S. infants and children receive vaccines like polio and MMR that have been available for a long time. In fact, about 90% of U.S. infants and young children get all doses of most recommended vaccines.

BACKGROUND: In the United States, vaccine safety is constantly monitored using the Vaccine Adverse Event Reporting System (VAERS), co-sponsored by CDC and the FDA. VAERS collects and analyzes reports of adverse events (possible side effects) that happen after vaccination. VAERS is an early warning system to alert researchers to possible side effects, but the system is not set up to determine whether reported events are actually associated with receiving a particular vaccine. Other types of studies can answer this question. The Vaccine Safety Datalink (VSD), a network of 8 managed care organizations with data for more than 9 million people, is often used for such studies. The VSD is not only used to follow-up on possible side effects noted in VAERS, but it is also used independently in ongoing studies of vaccine safety after vaccines are approved and in use.

CURRENTLY: According to VAERS, an increased risk of intussusception may be possible in the first week after receiving the first dose of RotaTeq. A VSD study is being done to see if RotaTeq is associated with intussusception. It includes data on more than 800,000 total doses of the vaccine. This study has not found a risk of intussusception. However, the VSD study cannot rule out a risk of intussusception with RotaTeq as low as the risk currently reported with Rotarix in the Mexico study.

RotaTeq, made by Merck, has been available in the United States since February 2006. About 27 million doses have been distributed.