By Genevra Pittman
NEW YORK (Reuters Health) - Despite concerns that rotavirus vaccines might raise infants' risk of blocked bowels, a new study finds that hospitalization rates for the intestinal complication didn't go up after vaccination became routine in the United States in 2007.
A version of the vaccine, which protects babies against diarrheal disease, was first released in the U.S. in 1998, but pulled from the market the next year following reports of intussusception -- when one part of the intestine slides inside another part -- in babies who'd recently been vaccinated.
When studies of newer versions of the live vaccine, which is taken orally, didn't find a link to the bowel problem, rotavirus vaccination was re-introduced in the U.S.
But surveillance for intussusception cases has continued, to see if slight risk increases that might only show up in a very large population are detected - a type of research that is typical after drugs and vaccines go on the market.
"The rotavirus vaccine appears to be very safe," said Dr. Joseph Zickafoose, from the University of Michigan in Ann Arbor, who worked on the study.
Zickafoose and his colleagues consulted a nationally-representative database of kids discharged from more than 4,000 hospitals in the U.S. over the decade before the vaccine was re-introduced, and one year shortly after.
They found that from 1997 to 2006, the number of babies hospitalized for blocked intestines seemed to drop slightly, from about 42 out of every 100,000 infants to 37 out of 100,000.
And in 2009, after the rotavirus vaccine was re-introduced, that pattern of decline continued: an estimated 33 out of every 100,000 infants were discharged after treatment for the bowel problem, the researchers report in the Archives of Pediatrics & Adolescent Medicine.
Recent studies from Mexico and Brazil suggested that one out of every 50,000 babies or fewer might get intussusception after being vaccinated for rotavirus, Zickafoose said.
"We expected even with that small amount of risk, we might see something show up after immunization had gotten started" in the U.S., he told Reuters Health.
His team couldn't tell which babies in the study had or hadn't been vaccinated for rotavirus before they were hospitalized, but he said the findings suggest the vaccine hasn't caused an overall increase in intussusception cases across the country.
Dr. Umesh Parashar, a rotavirus vaccine expert at the U.S. Centers for Disease Control and Prevention, said a very small extra risk of intussusception with the vaccine -- like that seen in Mexico and Brazil -- might be hard to pick up in this type of national study, which mostly catches intestinal problems not related to vaccination.
"The possibility of a lower-level risk certainly remains," said Parashar, who was not involved in the new research.
"I don't think that this analysis alone can prove or disprove an association. It is however reassuring to an extent to see that at least there's no major increase in intussusception," he told Reuters Health.
Zickafoose and Parashar agreed that even if there are very small risks associated with the rotavirus vaccine, the benefits of preventing diarrheal disease would outweigh them.
It's estimated that the vaccine prevents 30,000 to 40,000 infant rotavirus hospitalizations each year, according to Parashar. If the extra intussusception risk seen in other countries applies in the U.S., the vaccine would only cause 40 to 60 annual hospitalizations for the bowel problem.
The vaccine is currently recommended for all babies, who get two or three doses by the time they're six months old, depending on the brand of the vaccine.
Based on the new findings, Zickafoose said, parents should continue to feel safe getting their children vaccinated, and policy makers can feel good about recommending vaccination.
"We are fairly confident that we are not looking at a very high risk," Parashar said. "And if it's a low-level risk of this magnitude, in the context of this benefit, it definitely supports continued vaccination."
SOURCE: http://bit.ly/A4V9G6 Archives of Pediatrics & Adolescent Medicine, online January 2, 2012.