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Children's Vaccines Health Center

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Combo Vaccine Raises Risk of Seizures in Toddlers?

Safer to give MMR and chickenpox shots separately for first dose, researchers say

WebMD News from HealthDay

By Amy Norton

HealthDay Reporter

MONDAY, June 9, 2014 (HealthDay News) -- Toddlers who get a newer vaccine that fights four infections in one jab have a slightly increased risk of fever-induced seizure, a large new study confirms.

At issue is a vaccine that targets measles, mumps, rubella and varicella (chickenpox) in one shot, instead of giving the traditional MMR and varicella vaccines separately.

In theory, one shot sounds better than two. But in the new study, 1-year-olds who received Priorix-Tetra -- the MMRV vaccine used in Canada -- were twice as likely to develop a fever-related seizure as children who got separate MMR and chickenpox shots.

The findings are in line with a 2010 study of the MMRV vaccine used in the United States, known as ProQuad.

In the United States, parents now have to explicitly ask for the MMRV if they want their toddler to have it, said Dr. Nicola Klein, who led the ProQuad study.

But even with the increased risk posed by the MMRV vaccine, the odds of a brief, fever-related seizure are extremely low.

And the seizures aren't dangerous, "though they are scary for parents," said Klein, co-director of the Kaiser Permanente Vaccine Study Center in Oakland, Calif.

She said children are actually much more likely to suffer a high fever and seizure if they were to catch the measles.

"Get your child vaccinated," she stressed. "We're in the middle of a 20-year high in measles cases."

Fevers are part of the immune system response, whether to infection or vaccination.

It's not clear why the MMRV is more likely to cause a fever-related seizure than the separate shots, said Shannon MacDonald, a post-doctoral fellow at the University of Calgary in Alberta, Canada, who led the new study. But one theory maintains the combined vaccine triggers a stronger immune response and a higher fever in some children, which makes a seizure more likely.

MacDonald's findings, published online June 9 in CMAJ (Canadian Medical Association Journal), are based on records for almost 278,000 Alberta children between the ages of 12 and 23 months. The children received either the MMRV or separate MMR and chickenpox shots on the same day.

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