On Mar. 14, 2008, the U.S. Centers for Disease Control and Prevention (CDC) updated its recommendations for administering combination MMRV vaccine.

ACIP also recommended establishing a work group to conduct in-depth evaluation of the findings regarding the increased risk for febrile seizures after the first dose of MMRV vaccine to present for consideration of future policy options.

The Vaccine Safety Datalink (VSD), which routinely monitors vaccine safety by near real-time surveillance using computerized patient data, detected a signal of increased risk for seizures of any etiology among children aged 12–23 months after administration of MMRV vaccine compared with administration of MMR vaccine (many children also received varicella vaccine).

When children who received MMRV vaccine were compared with children who received MMR vaccine and varicella vaccine administered at the same visit, statistically significant clustering of seizures was observed 7–10 days after vaccination in both groups. Medical records were reviewed to validate the diagnosis, and a multivariate logistic regression was used to adjust for age and influenza season.