Published: May 13, 2013 | Updated: May 13, 2013

By Michael Smith , North American Correspondent, MedPage Today

Action Points

• Note that this registry-based study revealed an extremely low risk of intussusception occurring in children after rotavirus vaccination.
• Be aware that, prior to the introduction of vaccination, rotavirus was the most common cause of diarrhea in infants and led to substantial morbidity and mortality.

The risk of intussusception from rotavirus vaccination is less than one in 100,000, researchers reported.

Analysis of a large database of reported cases found a “persistent clustering” of intussusception 3 to 6 days after the first dose of the pentavalent RotaTeq (RV5) vaccine, according to Penina Haber, MPH, of the CDC, and colleagues.

But the rate is so low that, if every child eligible for the vaccine got inoculated, it would add about 33 extra cases of the bowel condition every year, Haber and colleagues reported online and in the June issue of Pediatrics.

The findings come from analysis of cases of intussusception in vaccinated infants reported to the Vaccine Adverse Event Reporting System (VAERS) over a 7-year period since the RV5 vaccine was introduced in 2006, Haber and colleagues reported.

They also looked at cases reported after vaccination with the monovalent Rotarix (RV1) vaccine, but did not quantify the risk because the medication has been less widely used.

The background rate of intussusception is about 35 cases per 100,000 infants yearly, according to a 2008 study published inPediatrics. Against that, CDC figures showthat — before the introduction of vaccines — rotavirus led annually to 410,000 physician visits, up 272,000 emergency department visits, up to 70,000 hospital admissions, and between 20 and 60 deaths.

Previous research, including clinical trials, has found little evidence of an increased risk of the condition with the current vaccines, but there has been some evidence from post-licensure studies in Australia and Mexico of a risk in the range of one to two cases per 100,000 vaccinations, Haber and colleagues noted.

To try to clarify the situation, Haber and colleagues looked at cases reported to VAERS from February 2006 through April 2012 for RV5 and from April 2008 through April 2012 for RV1.

They used a self-controlled risk interval analysis that compared rates of reports 3 through 6 days after the shot — when the vaccine virus is at its peak of replication — with those filed in days zero, one, and two.

The system got 584 confirmed intussusception reports after RV5 shots. The daily reporting ratio comparing the two periods after the first dose was 3.75 with a 95% confidence interval from 1.90 to 7.39.

There was no significant difference in reporting during the two periods after dose two or dose three, the researchers found.

Over all three doses, the excess risk of intussusception was 0.79 per 100,000 vaccinations, they concluded.

The system also got 52 reports of intussusception after RV1 vaccination, with clustering 3 to 6 days after the first shot.

The study allows clinicians to understand both the “risk side and benefit side” of rotavirus vaccination, commented Andrew Pavia, MD, of the University of Utah in Salt Lake City.

On one hand, he told MedPage Today, the risk turned out to be small and should be set against more than 100,000 hospital admissions every year.

On the other hand, the statistical approach used by Haber and colleagues has some built-in “errors and assumptions” that affect its accuracy. Nevertheless, Pavia said, the methods allow measurement of “very low risks that can’t be determined even in very large clinical trials.”