Although some data have suggested a possible increased risk of intussusception after administration of the pentavalent rotavirus vaccine in infants, a published analysis that included almost 800,000 doses administered to U.S. infants found no increased risk of the condition following vaccination.
In background information for the study, which appears in the Feb. 8 edition of JAMA, the authors wrote that the rhesus tetravalent rotavirus vaccine was withdrawn from the U.S. market in 1999 because of a significantly increased risk of intussuception (when a portion of the small or large intestine slides forward into itself, like a telescope) following vaccination.
Since then, two vaccines to prevent rotavirus infection — a pentavalent rotavirus vaccine (RV5, RotaTeq) in 2006 and a monovalent rotavirus vaccine (RV1, Rotarix) in 2008 — have received licensing for use in the United States. No increased risk of intussuception was observed in large prelicensure trials, but an increased risk was observed in two recent international postlicensure trials in the week after administration of the first dose of rotavirus vaccines.
Irene M. Shui, ScD, of Harvard Medical School and Harvard Pilgrim Health Care Institute in Boston, and colleagues reexamined intussusception risk associated with rotavirus vaccination, with a specific focus on the one- to seven-day risk window after administration of the first dose. The study included infants ages 4 to 34 weeks who were enrolled in the Vaccine Safety Datalink and received RV5 between May 2006 and February 2010.
During that time, 786,725 doses of RV5 were administered. Of these, 39% were first doses, 33% were second doses and 28% third doses. The comparison cohort included 389,026 visits.
The researchers found there were no statistically significant increased risks for intussusception in either the one- to 30-day risk window or the one- to seven-day window for all doses combined or in dose-specific analyses, after adjusting for age.
For the one- to 30-day window following all RV5 doses, there were 21 cases of intussusception compared with 20.9 expected cases. Following dose 1, there were seven cases compared with 5.7 expected cases. For the one- to seven-day window following all RV5 doses, there were four cases compared with 4.3 expected cases; for dose 1, there was one case compared with 0.8 expected cases.
“Based on our analysis, an excess risk of one intussuception event per 65,287 RV5 vaccines following dose 1 can be reliably excluded, although we cannot rule out the possibility of a lower-level risk,” the authors wrote.
The researchers add that the reasons for the inconsistent results between different studies are unclear, but some of the inconsistency may stem from the location of the trials. The two recent postlicensure trials in which an increased risk was observed took place in Australia and Mexico.
“Because intussuception is a rare event, we cannot rule out a chance finding of risk in Australia and Mexico as well as the possibility of not detecting a low-level risk in the United States and Brazil,” the authors wrote. “Another possible explanation might be effect modification of the rotavirus vaccine-intussusception association by an environmental or genetic factor that differs between the populations.”
In conclusion, the authors wrote, the “introduction of rotavirus vaccines has had a substantial public health effect on severe rotavirus disease in U.S. infants. 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.”
To read a study summary and access the study via subscription or purchase, visit http://bit.ly/zMHHb2.