Fewer older children and adults were hospitalized for severe diarrhea once the U.S. started vaccinating babies against rotavirus in 2006, according to a new study.
Rotavirus is one cause of the "stomach flu," or gastroenteritis, and introduction of the rotavirus vaccine has already been tied to a drop in related hospitalizations among preschoolers. But whether vaccinating babies would also confer protection for older people was unclear, researchers said.
"This study confirms the benefits of the rotavirus vaccine program, but it also shows there's an unexpected benefit to the population at large," Ben Lopman, who worked on the study at the U.S. Centers for Disease Control and Prevention, said.
"This is one example of what we call herd immunity," he told Reuters Health.
"By vaccinating young children you prevent them from getting sick, but you also prevent them from transmitting (rotavirus) to their siblings and their parents."
The initial rotavirus vaccine was introduced in the U.S. in 1998 and pulled the following year due to concerns it might cause blocked bowels in babies.
Newer versions, which are given orally, became routine in 2007. Pre- and post-release testing of those vaccines has not shown those same side effects (see Reuters Health story of January 5, 2012 here: reut.rs/AAe8bT).
For their study, the CDC researchers compared data on a nationally-representative sample of hospital stays by children and adults diagnosed with rotavirus or unspecified gastroenteritis in 2000-2006 and 2008-2010.
Rotavirus testing is rarely performed in adults, they noted, so many more unspecified gastroenteritis cases were included.
As previous studies have shown, rotavirus rates among young children dropped after the start of vaccination; there were 80 percent fewer discharges for rotavirus among kids under five in the post-vaccine study years than in pre-vaccine years.
Rotavirus-related discharges also dropped by 70 percent for children aged five to 14, by 53 percent for 15- to 24-year-olds and by 43 percent among adults aged 25 to 44.
Likewise, discharges for cause-unspecified gastroenteritis fell by 30 percent among five- to 14-year-olds after 2007, by 11 percent among teenagers and young adults and by six percent for adults under 45.
Although it's not clear how many of those unspecified cases were caused by rotavirus, reductions were primarily seen in March and April - the peak months for rotavirus hospitalizations before the vaccine, the researchers wrote Tuesday in the Journal of the American Medical Association.
"The pattern that we've seen after the introduction of vaccines is very consistent," Lopman said.
He said prior estimates showed between 55,000 and 70,000 young children were hospitalized for rotavirus every year before 2006.
"The benefits of the vaccine have been demonstrated time and again," he said.
"Increasing vaccine coverage could bring even more benefit from what has occurred to date."