Drugmaker GlaxoSmithKline has received federal approval for a vaccine to stop the leading cause of diarrhea in infants, a market dominated by rival Merck.

The Food and Drug Administration on Thursday approved the company's Rotarix vaccine to prevent the rotavirus in infants, the company said in a statement.

Rotarix is given in a two-dose oral regimen that can be completed by the fourth month after birth. Merck already markets a similar product, Rotateq, which is usually given in three doses over the course of six months. Rotateq was Merck's second-best selling vaccine last year with revenue of $525 million.

Len Friedland, Glaxo's clinical director for vaccines, suggested Thursday its vaccine would be more convenient for parents than Merck's because it can be completed in fewer visits to the doctor's office.

FDA cleared the vaccine, which is made from a weakened strain of the virus, based on testing in 75,000 infants. Those results showed no evidence of life-threatening intestinal problems seen with the first rotavirus vaccine approved in the U.S. That vaccine, RotaShield from Wyeth, was pulled from the U.S. market in 1999 after it was linked to an increase in intussusception, a twisting of the intestines.

Whitehouse Station, N.J.-based Merck added language about intussusception to Rotateq's label last year after receiving 28 reports of children developing the disorder. The FDA said the reports did not exceed the number expected to occur naturally each year.

While Glaxo's vaccine currently contains no language about intussusception, Friedland said that may change after it has been on the market.

"This is a disease that occurs naturally in children and I expect there will be reports of it with our vaccine as there have been with Merck's," Friedland said.

Glaxo is currently negotiating terms of a follow-up study with FDA to track the vacinne's safety in the U.S. The FDA based its approval of Rotarix on studies in South America, Europe, Asia and Africa.

About 55,000 U.S. children are hospitalized each year due to the rotavirus, according to the Centers for Disease Controls. The U.S. government and several medical societies recommend vaccination for all infants.

Despite FDA's approval Thursday, Glaxo does not expect the vaccine to gain widespread use until June, when the government's committee on immunization meets to recommend new vaccines.

Shares of London-based GlaxoSmithKline PLC rose 21 cents to close at $44.72 on Thursday.