June 27, 2009

Rotavirus Vaccines Shift Course of Diarrhea-Causing Disease

Cluster of round rotavirus particles Electron micrograph of rotavirus particles. Dr. Erskine Palmer, CDC.

New vaccines can prevent or temper epidemics of a leading childhood diarrhea-causing disease, help protect the unvaccinated and raise the age at which the infection first appears in children, researchers reported.

Rotavirus is the leading cause of severe acute gastroenteritis (vomiting and diarrhea) among children worldwide. In the United States, researchers noted that winter outbreaks have historically begun in the Southwest and come later to the Northeast. This contrasts with other seasonal infections, such as flu. Flu epidemics tend to begin in cities and spread to less populous areas. The rotavirus pattern, however, has recently become less pronounced, with epidemics coming later in southwestern states.

Rotavirus vaccines, first introduced in 2006, have been shown to be very effective against rotavirus disease, preventing up to 74% of all rotavirus cases, 98% of severe cases and 96% of hospitalizations. Seeking insights into the worldwide benefits of rotavirus vaccination, a team of researchers set out to study the spread of disease before and after vaccination became available in the United States, where the disease is rarely fatal.

Mathematical modeling and analysis was done by scientists from NIH's Fogarty International Center (FIC), the Centers for Disease Control and Prevention (CDC), the Agency for Healthcare Research and Quality and others. Support also came from NIH's National Institute of General Medical Sciences (NIGMS), the Department of Homeland Security and others. The modeling took into account regional birth rates and predicted vaccination levels and effectiveness. Data from 2007-2008, when vaccination first reached appreciable coverage levels in the country, were used to validate the model.

The results appeared in the July 17, 2009, issue of the journal Science. The model suggests that when 80% or more of children in a population are vaccinated, annual epidemics will occur on a less regular basis and more unvaccinated children will be protected. Infections will also make their first appearance in children when they are older than the previous norm of less than 5 years of age. A later onset would likely mean fewer cases and less severe symptoms.

The study also showed for the first time that the timing of rotavirus epidemics is dependent on the birth rate in the population. That's because epidemics are driven by infants who have never been infected before. The higher birth rates of the Southwest relative to the Northeast account for the earlier winter outbreaks there.

“Rotavirus vaccines have rapidly and dramatically reduced hospitalizations and emergency room visits for gastroenteritis in American children,“ says investigator Dr. Umesh D. Parashar of the CDC. ”This research not only explains the effects of the U.S. rotavirus vaccination program, but also lays the foundation for understanding the tremendous life-saving benefits of vaccination in the developing world, where more than half a million children die from rotavirus each year.”

“Each population is going to have a different demographic makeup, and there may be conditions we cannot predict with certainty, but we believe introducing vaccination in the developing world will decrease the terrible burden of rotavirus,” says lead author Dr. Virginia Pitzer of Penn State and FIC.

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