WASHINGTON (Reuters) - Rotavirus vaccines made by GlaxoSmithKline Plc and Merck & Co Inc are safe to use despite being contaminated with a pig virus, U.S. health regulators ruled on Friday.

The Food and Drug administration, in a statement, said it was safe for doctors to resume giving patients Glaxo’s Rotarix and continue using Merck’s Rotateq. The agency said there was no evidence the contamination caused any harm and the vaccines were important in preventing hospitalizations and death.

Rotavirus can cause fatal diarrhea. Both vaccines target the virus, but pieces of DNA from porcine circovirus (PCV) have been found in both companies’ products.

The FDA’s decision follows a May 7 recommendation by its advisory panel, which ruled that the risk to humans from the pig virus was theoretical at best. It called for continued use of the vaccines, saying their benefits outweighed any potential risk.

Some strains of the pig virus are believed to cause a wasting syndrome in young piglets, marked by diarrhea and an inability to gain weight, but they are not known to injure humans. Tests found DNA from the virus in master cells used to make the Glaxo’s product.

Glaxo officials have said the DNA may have come from a pig-derived enzyme called trypsin used early in development. The company has said there is no manufacturing or safety issue with its vaccine. Merck has also said its product is safe.

Neither vaccine is a blockbuster product.

Sales of Merck’s vaccine totaled $522 million in 2009, including $468 million in the United States. Glaxo’s rotavirus vaccine sales in 2009 were $440 million globally, including $118 million in the United States.

Worldwide, rotavirus kills more than 500,000 infants each year, mostly in low- and middle-income countries. Deaths are rare in the United States, but severe illness that requires a hospital stay is possible.

Glaxo’s vaccine won U.S. approval in 2008.