(HealthDay News) — One-year-olds who receive Priorix-Tetra — the measles-mumps-rubella-varicella (MMRV) vaccine used in Canada — are twice as likely to develop a fever-related seizure as children who receive separate MMR and varicella vaccines, according to research published online June 9 in CMAJ, the journal of the Canadian Medical Association. The findings are in line with a 2010 study of the MMRV vaccine used in the United States, known as ProQuad.

Shannon MacDonald, PhD, RN, of the University of Calgary in Alberta, Canada, led the new study. The findings are based on records for almost 278,000 Alberta children between the ages of 12–23 months. The children received either the MMRV or separate MMR and varicella vaccines on the same day.

The researchers found that children’s seizure rate peaked 7–10 days after they were vaccinated. At that point, there were almost 6 seizures for every 10,000 doses of the MMRV, vs. 2 seizures for every 10,000 doses of the separate vaccines.

The authors note that, based on the ProQuad study, the U.S. Advisory Committee on Immunization Practices changed its stance on the MMRV. Now it says that unless parents ask about the combined vaccine, doctors should default to separate shots for young children getting their first dose of the MMR and varicella vaccines. In general, fever-related seizure is uncommon at ages 4–6 years, the age at which second dose is typically given, and the advisory committee says the MMRV is the better option for the second dose.

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