Newly introduced vaccines may result in less frequent and less severe outbreaks of a virus that causes more than half a million deaths worldwide.

Rotavirus can cause severe diarrhea and can be fatal. Contracted from eating or drinking fecal-contaminated food or water, it is a major cause of illness and death, especially among young children in the developing world.

Two new vaccines - recently introduced in North America and Europe - have been shown to prevent severe diarrhea in infants.

In a new study in the journal Science, researchers used a mathematical model to estimate the effects in the United States of different vaccination rates.

According to the model, when 70 to 80 percent of U.S. children are vaccinated, rotavirus outbreaks would go from being an annual occurrence to happening every other year. At higher vaccination rates, several years would go by with very few cases of severe diarrhea.

In a Science magazine podcast, lead author Virginia Pitzer of Penn State University explained that as vaccination rates increase, the average age of children with severe diarrhea would also increase.

"If those infections occur later in life, then [it] could be that it also leads to less severe disease," she says, because "it's easier to treat a 5-year-old with diarrhea than it is to treat a 1-year-old."

Pitzer also says according to the model, the vaccine's benefits extend beyond those who get it.

"It essentially shows that individuals who don't receive the vaccine might receive some benefit because the people?who are vaccinated are less likely to spread the infection," she says.

Pitzer cautions that the rotavirus vaccines may not work quite the same way in developing countries, which may have different strains of the virus. And malnutrition and other diseases can affect the vaccine's performance. Studies are underway in Asia and Africa to examine how well the vaccine works in those regions.

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