Post-licensure Monitoring of Intussusception (IS) after RotaTeq® Vaccination -- Vaccine Adverse Event reporting System (VAERS) 3/2006-1/2008

Learning Objectives for this Presentation:
By the end of this presentation, participants will identify the systems used to monitor the safety of RotaTeq®) as part of post-licensure surveillance, and name the adverse event that has been under closest surveillance.

Background:
In 1999, a previous rotavirus vaccine (Rotashield) was withdrawn from the US market after post-licensure monitoring identified that it caused intussusception (IS). In February 2006, a new rotavirus vaccine (RotaTeq®) was approved for routine vaccination of US infants. Although RotaTeq® has not been associated with IS in large pre-licensure trials, as the vaccine is administered to more infants under conditions of routine practice, safety monitoring is critical.

Objectives:
To assess the safety of RotaTeq®) vaccine.

Methods:
We reviewed IS reports after RotaTeq®) vaccination reported to the Vaccine Adverse Events Reporting System (VAERS). VAERS is a national passive reporting system. The number of reported IS cases in VAERS was compared with the expected number based on dose distribution data from the manufacturer and age-adjusted background rates of IS (based on ICD-9 codes) from the Vaccine Safety Datalink (VSD).

Results:
From 3/1/2006 through 9/25/2007, VAERS received 160 confirmed IS reports. Twenty-seven and 47 IS cases were reported to VAERS within 1-7 and 1-21 days post vaccination, respectively, compared with expected numbers of 50 and 151 IS cases within 1-7 and 1-21 days. Thus, the IS reporting rate ratios in VAERS were 0.51 (95% CI 0.32-0.82) for 1-7 days and 0.30 (95% CI 0.20-0.44) for 1-21 days.

Conclusions:
IS reports to VAERS after RotaTeq™ vaccination does not exceed the number expected to occur by chance alone. However, because of VAERS underreporting, uncertain applicability of VSD background rates to the vaccinated population, and use of doses distributed instead of doses administered, some increased risk of IS rarer than that seen with Rotashield® could not be excluded; safety monitoring is ongoing.