newscientist | The US Food and Drug Administration (FDA) has reported that stocks of Merck's Rotateq vaccine against rotavirus are contaminated with the pig viruses PCV1 and PCV2. But the agency has not advised doctors to stop using it as the pig viruses aren't known to cause disease in humans, and rotavirus kills roughly half a million infants worldwide each year. An FDA advisory panel said the vaccine's benefits still outweigh its risks.

The FDA plans to monitor recipients for pig virus-related illness. "There will be quite careful monitoring of the people that have received the vaccine and I think that's entirely appropriate," says virologist Stephen Hughes, who advised the FDA on the issue.

Rotavirus vaccines are mainly given to infants in the developing world, where the virus is most likely to kill. In March, a separate rotavirus vaccine, Rotarix, made by GlaxoSmithKline was found to contain PCV1. In that case, the FDA recommended that doctors avoid using Rotarix while it gathers evidence, but the FDA now says it will issue new recommendations on both affected vaccines soon.