The MMRV vaccine, which has been used since 2005 to reduce the number of injections that children receive and improve vaccine compliance, will now be recommended only for children ages 4 and older. The changes to the MMRV vaccine recommendations were made in response to data indicating that young children who receive the combined vaccine have a slightly increased risk of febrile seizures — or harmless convulsions in young children caused by a fever. However, according to CDC data, febrile seizures as a result of the MMRV vaccine were rare, occurring in about eight out of every 10,000 doses administered. Only a small percentage of young children in the U.S. — about 15% — receive the combined MMRV vaccine as a first dose. Kulldorf defended the decision to limit use of the MMRV vaccine, arguing that it would help restore trust in public health measures.