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Two separate unpublished studies have confirmed an association between the first dose of the combination MMR-Varicella (MMRV) vaccine and an increased risk of febrile seizures.
The MMRV vaccine is called ProQuad and is manufactured by Merck. One of the studies was sponsored by Merck, and the other was done by the Centers for Disease Control (CDC) in what is known as the Vaccine Safety Datalink (VSD) Project. The CDC safety study among children aged 12 to 23 months detected a cluster of cases of febrile seizure seven to 10 days after vaccination.