Rotavirus causes severe diarrhea that kills more than a half-million people each year, mostly very young children. A recently-introduced vaccine has proved to be very effective and has shown some unexpected benefits, extending protection beyond the children who received the vaccinations.
Rotavirus fatalities are rare in the United States, but the disease does send tens of thousands of children to the hospital each year.
Nationwide vaccinations began in the U.S. in 2006, and now researchers are evaluating the results.
They already know that the vaccine is effective, with diarrhea-related hospitalizations down 50 percent just two years after the immunization program started. But researcher Ben A. Lopman, with the U.S. Centers for Disease Control and Prevention, says the protection went far beyond the children who actually got vaccinated.
"The vaccine program also was providing indirect protection against hospitalizations in older children, and adults and in the elderly. [There] were fewer hospitalizations in 2008 - over 10,000 fewer hospitalizations in these older age groups - than in previous years."
This indirect protection - sometimes called herd immunity - occurs when there are fewer people to pass around an infection, as Lopman explains.
"The idea here is that by vaccinating young children, you stop them from transmitting infection to their older siblings, their parents, their grandparents, etc., because those children themselves are not becoming infected because they've been vaccinated."
There's another surprise here - that older children and adults were getting rotavirus infections in significant numbers. While the vaccine is only recommended for young children, Lopman says his study suggests that doctors should be aware that patients with rotavirus symptoms may be infected, regardless of age.
Although this study was done in the United States, rotavirus is a much more serious problem in low- and middle-income countries, and the vaccine hasn?t been as effective in those areas. So Lopman says he can't say if his findings would apply there.
"The kinetics of rotavirus transmission are very different in low-income settings, where there seems to be just much more rotavirus around. So it's not clear at this stage whether these indirect benefits would be afforded in low-income settings or not."
In a commentary published with the research paper, a senior official of the U.S. National Institutes of Health, Roger I. Glass, director of the NIH Fogarty International Center, says more research is needed to measure the effectiveness of a rotavirus vaccination program conducted where the disease is a much more serious threat. But the official writes that Lopman's study suggests the indirect protection benefit should be considered in assessing the value of a vaccination program.
The research study by Ben A. Lopman and colleagues is published online by the Journal of Infectious Diseases.