Postlicensure Monitoring of Intussusception After RotaTeq Vaccination in the United States, February 1, 2006, to September 25, 2007

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Abstract
BACKGROUND. In 1999, a previous rotavirus vaccine (RotaShield; Wyeth Laboratories, Marietta, PA) was withdrawn from the US market after postlicensure monitoring identified an association with intussusception. Although the new rotavirus vaccine (RotaTeq; Merck, West Point, PA) introduced in 2006 was not associated with intussusception in prelicensure trials, additional monitoring is important to ensure a complete safety profile. METHODS. We assessed intussusception reports after RotaTeq vaccination by using data from the Vaccine Adverse Event Reporting System and the Vaccine Safety Datalink, a cohort of children enrolled in managed care. Observed versus expected rate ratios were determined by using vaccine dose distribution data and Vaccine Safety Datalink background intussusception rates. RESULTS. Between February 1, 2006, and September 25, 2007, the Vaccine Adverse Event Reporting System received 160 intussusception reports after RotaTeq vaccination. With the assumptions that reporting completeness was 75% and that 75% of the distributed doses of RotaTeq were administered, the observed versus expected rate ratios were 0.53 and 0.91 for the 1–21 and 1–7 day interval after vaccination, respectively. In the Vaccine Safety Datalink, 3 intussusception cases occurred within 30 days after 111521 RotaTeq vaccinations, compared with 6 cases after 186722 non–RotaTeq vaccinations during the same period. If, like RotaShield, RotaTeq had a 37-fold increased risk of intussusception within 3 to 7 days after vaccination, then 8 intussusception cases would be expected within 3 to 7 days among the ∼84000 infants vaccinated with the first dose of RotaTeq in the Vaccine Safety Datalink (N = 49902) and the prelicensure trial (N = 34035) combined, whereas no cases have been observed. CONCLUSIONS. Available data do not indicate that RotaTeq is associated with intussusception. Although an intussusception risk similar in magnitude to that of RotaShield can be excluded, continued monitoring is necessary for complete assessment of the safety profile of RotaTeq.