Age of Administration and Safety of Measles-Containing Vaccines

Measles (M)-containing vaccines, when administered to children aged 12 to 23 months, are associated with increased risk for fever and febrile seizures 1 to 2 weeks after immunization. In the U.S., the only M-containing vaccines are measles, mumps, and rubella (MMR) and measles, mumps, rubella, and varicella (MMRV); the first dose is administered at 12 to 15 months, and the second at 4 to 6 years. The risk for febrile seizures 1 to 2 weeks following immunization is twice as high with MMRV as with separately administered MMR and V preparations. Between ages 12 and 23 months, the background rate of febrile seizures peaks at 16 to 18 months.

To determine the risk for fever and seizures following immunization with M-containing vaccines at various ages, researchers analyzed data from the Vaccine Safety Datalink (VSD) — a collaborative effort between the CDC and 10 managed-care organizations. The analysis involved records for 840,348 children who had received M-containing vaccine at ages 12 to 23 months between 2001 and 2011.

A total of 18,403 fever episodes and 1810 seizure events occurred during the 42 days postvaccination. The relative risk for fever and seizures 7 to 10 days postvaccination (the time of greatest risk) was significantly higher in children aged 16 to 23 months than in those aged 12 to 15 months. When the 7- to 10-day risk interval was compared with a control interval, the attributable risk for seizures — but not fever — during the risk interval was significantly greater in the older group.