A child receives a dose of oral vaccine for rotavirus

From Medical Correspondent Rhonda Rowland

(CNN) -- A new vaccine is now available for rotavirus, a largely undiagnosed virus that affects almost every child in the world by age four.

The symptoms of rotavirus are not usually intense, so parents often don't know their child is affected, but up to 100,000 children each year in the United States are hospitalized with severe cases of the disease.

The parents of 11-month-old Jim Stewart say they were extremely concerned when their son's rotavirus infection sent him to the hospital for a weekend.

"On a Tuesday morning he started vomiting, by Wednesday the diarrhea started and it was just very obvious he did not feel well. He's a very active baby and he became very listless, very lethargic."

Doctors say children who go to day care facilities are most at risk for rotavirus infection.

"It's spread through what's known as fecal-oral route, " says pediatrician Dr. Bruce Bessey. "Essentially someone with dirty hands who maybe just changed a diaper."

But now a rotavirus vaccine is available that should protect children against the most severe cases of the disease. It's given orally at two,four, and six months of age.

Peak season for the virus is during the fall and winter months.

So far, groups that make vaccine recommendations -- such as the Centers for Disease Prevention and the American Academy of Pediatrics have not taken a stand as to who should get the rotavirus medication.