ATLANTA — No major safety issues have arisen thus far with the new rotavirus vaccine, Penina Haber said at a meeting of the Centers for Disease Control and Prevention's Advisory Committee on Immunization Practices.
In fact, rates of intussusception—the complication that resulted in the 1999 withdrawal from the market of the old rotavirus vaccine (Wyeth-Ayerst's RotaShield)—are actually lower with Merck's Rotateq than would be expected in the general population, said Ms. Haber, an epidemiologist with the CDC's Immunization Safety Office.
The CDC is monitoring Rotateq for gastrointestinal-related adverse events as well as any other unexpected problems via the passive Vaccine Adverse Event Reporting System (VAERS). Should any safety “signals” arise, the active surveillance system known as the Vaccine Safety Datalink (VSD), comprising eight large HMOs (covering 3% of the U.S. population), will be utilized to investigate further.
The CDC is now using VAERS and VSD to monitor safety for all new vaccines, with researchers from the CDC and the Food and Drug Administration reviewing all reports sent to VAERS on a daily basis, Robert L. Davis, director of the CDC's Immunization Safety Office, said during a joint presentation with Ms. Haber on vaccine safety.
From March 1, 2006, through Oct. 23, 2006, VAERS received a total of 189 adverse event reports following receipt of Rotateq, from a background of 1,786,476 doses distributed as of Sept. 30, 2006. Of the 189 reports, 48% were associated with receipt of Rotateq alone, and the rest were in combination with other vaccines. Children aged 2–3 months accounted for 57% of the reports, while 5% were for children under 2 months of age. (The vaccine is recommended at ages 2, 4, and 6 months.) Fifty-five percent of reports were of events occurring within 2 days of vaccination, while another 5% occurred within 7 days.
Among the most frequent adverse events following receipt of Rotateq in children up to 12 months of age were diarrhea (24% vs. 3% following all other vaccines), vomiting (22% vs. 5%), GI hemorrhage (7% vs. 0%), and melena (6% vs. 1%). A total of 30 (16%) of the reports were of serious events, including 6 cases of intussusception. Four occurred after dose 1 and two after the second dose, at an interval of 2–32 days following vaccination.
Calculated from the VSD background intussusception rate of 2.98 per 10,000 person-years, the expected number of cases within a 21-day period would be 30.7. In contrast, just four cases were observed within 21 days of Rotateq receipt. If an underreporting rate of 47% is assumed (Am. J. Epidemiol. 2001;154:1006–12), the number of intussusceptions associated with Rotateq would still be significantly lower than expected, Ms. Haber said.
Excluding the intussusception cases, there were 19 reports of hematochezia following Rotateq. During the same time period, hematochezia was reported in 4 children receiving other vaccines in 2,248 VAERS reports. Most of the hematochezia cases occurred within 3 days of vaccination, and none was serious. In addition to the approximately 96,000 infants born each year who are surveilled in VSD and will be followed for adverse events after administration of Rotateq, about 45,000 infants will provide additional data to Merck in a phase 4 study, she noted.