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4-in-1 Vaccine Ups Child Seizure Risk

Measles-Mumps-Rubella-Chickenpox Vaccine Doubles Febrile Seizure Risk
WebMD Health News
Reviewed by Louise Chang, MD

Feb. 26, 2008 -- ProQuad, Merck's 4-in-1 measles-mumps-rubella-chickenpox vaccine, doubles children's seizure risk compared with two separate MMR and chickenpox shots.

Even at twice the risk, 12- to 23-month-old children who get the vaccine have only a 1 in 2,000 higher chance of having a febrile seizure -- convulsions brought on by fever -- than those getting two separate shots.

Moreover, most U.S. children never had a chance to get the new 4-in-1 MMRV (measles-mumps-rubella-varicella) vaccine. Production problems have limited U.S. distribution. ProQuad won't be widely available before 2009, although some clinics may have a supply in hand.

A CDC safety study among children aged 12 to 23 months detected a cluster of cases of febrile seizure seven to 10 days after vaccination. The recommended age for a first dose of MMRV vaccine or for first doses of separate MMR and varicella vaccines is at 12 to 15 months.

Four out of every 10,000 kids who got separate MMR and varicella shots on the same day had a febrile seizure seven to 10 days later. Nearly twice as many kids who got ProQuad -- nine in 10,000 -- had febrile seizures seven to 10 days after vaccination.

Because the 4-in-1 ProQuad vaccine cuts down on the number of shots a child has to get, the CDC's Advisory Committee on Immunization Practices had recommended the vaccine over separate shots.

This changed after ACIP members heard the results of the CDC study, says John Iksander, MD, MPH, acting director of the CDC's Immunization Safety Office.

"The ACIP has now voted that there should not be a preference between choosing the combined vaccine and giving separate MMR and varicella vaccines," Iksander tells WebMD. "Once ProQuad is back in production, the recommendation should be clear that people can continue to use the separate vaccines, which is what I am now doing in my clinic, or to opt to use the combined vaccine."

Febrile Seizures: What to Do

About one in 25 children has at least one febrile seizure. It's a scary moment for parents. Most of these seizures happen on the first few hours of a child's fever.

According to the American Academy of Pediatrics, "The child may look strange for a few moments, then stiffen, twitch, and roll his eyes. He will be unresponsive for a short time, his breathing will be disturbed, and his skin may appear a little darker than usual."

Most of these seizures are over in under a minute, although rare cases may last for up to 15 minutes. Febrile seizures are rare in children younger than age 6 months or older than 3 years.

"The highest incidence is between 14 and 18 months of age," Iksander says. "That's right at the time we give them MMR and varicella vaccinations."

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