WASHINGTON (AP) – A vaccine that protects against a virus that is the leading cause of early childhood diarrhea – one that kills hundreds of thousands of infants in developing countries – received U.S. approval Friday.

Many poorer countries have been desperate for the rotavirus vaccine. But it’s unclear how quickly parents and doctors in the United States will embrace it: Seven years ago, the first attempt at a rotavirus vaccine ended in failure after it was linked to deaths and injuries.

The new vaccine, RotaTeq, made by Merck & Co., appears safe and effective, the Food and Drug Administration said. In trials involving tens of thousands of infants, it prevented at least 98 percent of severe cases of gastroenteritis, or intestinal inflammation.

“This vaccine gives health care providers an important new tool that can effectively prevent an illness that affects almost all children within the first few years of life,” said Dr. Jesse L. Goodman, director of the Food and Drug Administration’s Center for Biologics Evaluation and Research.

The earlier vaccine, Wyeth’s RotaShield, was pulled from the U.S. market in 1999 after it was linked to a small increase in intussusception, a rare, life-threatening blockage or twisting of the intestine. That could mean an initially cool reception for RotaTeq.

“I’m curious to see how quickly physicians will get back on the bandwagon,” said Scott Henry, an analyst at Oppenheimer & Co.

Trials of Rotateq, however, indicated it did not increase the risk of intussusception. But Merck officials have said they would conduct a follow-up study to track any long-term effects of their vaccine, which has been in development since 1993.

“That is a history of concern and that’s why we’re taking it seriously,” the FDA’s Goodman said in reference to the 20 deaths among the almost 1 million infants who received RotaShield. “Conversely, this is a disease that has great impact on children.”

In the United States, rotavirus sickens about 2.7 million children younger than 5, sends up to 70,000 to the hospital and causes 20 to 70 deaths each year.

A federal advisory committee on immunizations is to decide this month whether to add RotaTeq to the list of recommended pediatric vaccines, Merck said.

RotaTeq is a genetically engineered, three-dose oral vaccine that protects against five common rotavirus strains.

Merck seeks to license the vaccine in more than 50 countries. It also plans trials in Africa and Asia, where the virus is a noted killer. The vaccine requires refrigeration, which could complicate its use in poorer countries. Goodman said that was a “challenge” that had been met in other global immunization campaigns.

The liquid vaccine can be given orally to infants in three doses during regular well-baby visits to the doctor at two, four and six months.

“Virtually all children will experience rotavirus,” said Dr. Paul Offit of The Children’s Hospital of Philadelphia and co-creator of the vaccine. “While some children experience mild symptoms of rotavirus, infection can be severe and lead to dehydration that can be fatal.”

Merck officials have said the vaccine is meant to be effective for two years, because an older child who gets rotavirus is much less vulnerable to dehydration and other severe consequences of the illness, and therefore less likely to need hospitalization. Children would still probably catch rotavirus and develop natural immunities to it.

Friday’s approval should provide a boost for Merck, which faces thousands of lawsuits over its Vioxx painkiller. The vaccine will cost $62.50 a dose when ordered in 10-dose packets.

Side effects of the vaccine can include diarrhea, vomiting, ear infection, runny nose and sore throat, wheezing and coughing.

GlaxoSmithKline’s Rotarix vaccine has been licensed in Mexico but has not yet come up for approval in the United States.

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AP Business Writer Theresa Agovino in New York contributed to this report.

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On the Net:

Food and Drug Administration: http://www.fda.gov

AP-ES-02-03-06 1721EST