CDC, FDA studies link Merck and GSK rotavirus vaccines to bowel blockages

Merck's ($MRK) rotavirus vaccine RotaTeq has faced close scrutiny since winning FDA approval in 2006, with authorities monitoring whether it shares side effects with a similar Wyeth product that was pulled from the market. Now a FDA-funded study has shown RotaTeq is in fact linked to the side effect, but the benefits outweigh the risks.

Writing in the New England Journal of Medicine, FDA-funded researchers from Harvard Medical School and other institutions report 1.5 of 100,000 recipients of RotaTeq developed the side effect, a bowel disorder that can require surgery. A similar Center for Disease Control and Prevention (CDC)-backed study of GlaxoSmithKline's ($GSK) rotavirus vaccine, Rotarix, was published simultaneously and also noted the side effect. Around 5 out of every 100,000 recipients of Rotarix developed the disorder.     

Although the studies show both vaccines are associated with a significantly increased risk of the bowel blockage, called intussusception, neither is at the level that prompted the withdrawal of Wyeth's RotaShield. "In the case of RotaTeq, there is 1/10th of the risk of RotaShield. It's not zero, but it's not too much to worry about," Katherine Yih, lead author of the FDA study, told Bloomberg. The CDC found no increased risk for RotaTeq, while the FDA study was too small to assess Rotarix.

The writers of both papers called for the results to be viewed in light of the benefits of immunizing against rotavirus. Frank DeStefano, director of the CDC's immunization safety office, said the use of the vaccines has cut the number rotavirus-related hospitalizations by up to 50,000 cases a year. "The CDC continues to recommend that all infants get the vaccine," DeStefano said.

- read the Bloomberg article
- here's the CDC paper
- and the FDA research