Combination Vaccine Against Chicken Pox Raises Seizure Risk, But Just A Little

Medical assistant Elissa Ortivez draws an MMR vaccination at the Spanish Peaks Outreach Clinic on August 5, 2009 in Walsenburg, Colorado.
Medical assistant Elissa Ortivez draws an MMR vaccination at the Spanish Peaks Outreach Clinic on August 5, 2009 in Walsenburg, Colorado. John Moore/Getty Images

A vaccine against measles, mumps, rubella and chicken pox increases the odds for a fever-related seizure in young kids, but the risk is still very low.

A combination vaccine that protects young kids from measles, mumps, rubella and chicken pox all at once appears to increase the risk of temporary, fever-related seizures but not enough to worry about.

A recent study found that the combination vaccine, known as MMRV, doubles the risk for fever and seizures related to fever compared with a separate administration of the vaccine for measles, mumps, rubella (MMR) and the vaccine for chicken pox a week or so after immunization.

With the all-in-one vaccine, the risk is 1 additional fever-related seizure for every 2,300 doses, compared with two vaccines -- one against measles, mumps and rubella and another for chicken pox.

The risk that a child will suffer a seizure from either vaccine is low: less than one febrile seizure per 1,000 injections, according to Dr. Nicola Klein, who headed up the study by the Kaiser Permanente Vaccine Study Center. To put that number in perspective, it's less than the likelihood of the same kind of seizure being caused by a cold.

The results were based on the analysis of data for more than 400,000 children between 12 and 23 months old. The findings will be published in the July issue of Pediatrics.

Klein told Shots that febrile seizures are benign: "They do not lead to long term epilepsy or seizures but they can be frightening for parents." There's no increased risk for seizures beyond 7 to 10 days after a vaccination.

Scientists don't know why children who get the combo vaccine with protection against chicken pox are at a higher risk for fevers and seizures. But, now that the MMRV vaccine is coming back on the market this May after a previous shortage, Klein says her research group at Kaiser is going to keep monitoring the product. Copyright 2010 National Public Radio. To see more, visit http://www.npr.org/.

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