HealthDay News — Vaccination with the pentavalent rotavirus vaccine (RV5, Rotateq, Merck) did not increase intussusception risk among infants aged 4 to 34 weeks compared with infants who did not receive the vaccine, data indicate.

“With almost 800,000 doses of RV5 vaccine administered, including more than 300,000 first doses, we did not find an increased risk of intussusception following RV5 vaccination in either the one- to 30-day or one- to seven-day risk windows,” Irene M. Shui, ScD, from the Harvard School of Public Health in Boston and colleagues reported in the Journal of the American Medical Association.

An earlier rotavirus vaccine, the rhesus tetravalent rotavirus vaccine (Rotashield, Wyeth), was discontinued in 1999 due to an increased risk for intussusception. However, two newer rotavirus vaccines — RV5 and a monovalent rotavirus vaccine (RV1, Rotarix, GlaxoSmithKline) were introduced in 2008 after results from prelicensure trials did not indicate a greater risk for the intestinal disorder.

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Initial two-year post-licensure data from the U.S. supported those findings, but post-licensure data from Australia, Mexico and Brazil suggested the possibility of a low level of risk for intussusception with the two newer vaccines, mostly in the first week after the first dose in the series.

To further evaluate potential intussusception risk, researchers conducted a prospective cohort study using two additional years of data from the Vaccine Safety Datalink, which included 786,725 total RV5 doses, including 309,844 first doses, that were administered from May 2006 to February 2010.

There was no significant increase in the risk of intussusception the first week (RR=0.95; 95% CI: 0.37 to 2.63) or first 30 days (RR=0.90; 95% CI: 0.10 to 11.08) after RV5 vaccination, the researchers found. During the one- to 30-day window after vaccination, 21 intussusception cases were observed compared with an expected 20.9 cases (standardized incidence ratio [SIR]=1.01; 95% CI: 0.62 to 1.54). In the one- to seven-day window, four cases were observed compared with 4.3 expected cases (SIR 0.92, 95% CI 0.25 to 2.36).

During the one- to seven- day risk window after administration of the first RV5 dose, seven intussusception cases were observed versus an expected 5.7 (SIR= 1.21; 95% CI: 0.03 to 6.75), and in the one- to 30-day window, one case was observed versus an expected 0.8 cases (SIR=1.23; 95% CI: 0.50 to 2.54).

“Although we cannot entirely exclude the possibility of a very low-level risk, the findings of our study strengthen the evidence base in favor of vaccination for effective control of severe childhood rotavirus disease,” the researchers wrote. Rotavirus incidence has been steadily declining since the CDC issued recommendations in favor of routine childhood rotavirus vaccination.

The researchers are unsure what is causing the differences in intussusception rates among study populations in the Australia, Brazil, Mexico and the United States, but suggested that environmental or genetic factors could play a role.

Shui I, et al. JAMA 2012; 307:598-604.