The FDA estimates that 1 million U.S. kids have received the Rotarix vaccine.
The contamination was discovered by researchers developing a new technique for detecting viral material. GlaxoSmithKline confirmed that the pig virus, porcine circovirus type 1 or PCV-1, has been in the vaccine since it was developed.
This means that pig virus DNA was in the vaccine throughout clinical trials. No safety issues emerged from these international studies with 90,000 participants or, GlaxoSmithKline says, in post-marketing surveillance covering more than 69 million doses of the vaccine.
Nevertheless, as a precaution the FDA is asking doctors to stop using the two-dose Rotarix vaccine, which it approved in 2008.
"The message is clearly not a message of safety but of caution going forward," FDA Commissioner Margaret Hamburg, MD, said at a news conference. "We believe the vaccine is both safe and effective and we strongly encourage vaccination against rotavirus. But we want to more deeply understand the finding of this unexpected material in the product, and that is why we are putting a clinical pause on its use."
Alternative Rotavirus Vaccine Available
About 75% of U.S. doctors prescribe the three-dose RotaTeq vaccine, made by Merck, which was approved in 2006.
Because rotavirus causes severe diarrheal disease in infants, rotavirus vaccination begins at age 2 months. The FDA says children who already received one dose of the Rotarix vaccine should follow up with two doses of the RotaTeq vaccine. Those who already received two doses of Rotarix should be fully protected.
Merck's RotaTeq vaccine is made using a different process and is not contaminated with PCV-1.
It's not at all clear what it means to have found PCV-1 DNA in a vaccine. It's not yet clear whether the vaccine contains only fragments of the pig virus or whether the vaccine contains whole virus capable of replication.
PCV-1 does not cause disease in humans. It does not even appear to cause disease in pigs. According to GlaxoSmithKline, it's a common virus that's often eaten in meat products with no resulting illness.
To sort out these issues, the FDA is convening a panel of experts. The panel is expected to meet in four to six weeks and will be charged with advising the FDA on what to do next.
Meanwhile, GlaxoSmithKline is working to replace all contaminated Rotarix seed virus and the cell banks in which it is grown. But in the meantime, the company says in a news release, it will continue to manufacture the vaccine.
While rotavirus disease can be serious in developed nations, in the developing world it is a devastating diarrheal disease that each year kills a half million children. Benefits of the vaccine in these nations far outweigh its theoretical risks.
"While we investigate, we do have the luxury of an alternative product in this country," Hamburg said. "So while we are proceeding with a more in-depth investigation, clinicians in the U.S. should use the alternative product instead."
The issues with Rotarix, in which no safety issues have been seen, are very different from issues that arose with Wyeth's Rotashield vaccine. A year after its approval in 1998, Rotashield was linked to an increased risk of a serious bowel complication called intussusception. It was quickly taken off the market.
Studies find that neither GlaxoSmithKline's Rotarix nor Merck's RotaTeq rotavirus vaccines cause intussusception.