Small Increased Risk of Febrile Seizures with Combined MMRV Vaccine

By Megan Brooks

NEW YORK - A new study from Canada joins a prior study from the US in showing a slight increased risk of febrile seizures in children one to two years old who receive the combined measles-mumps-rubella-varicella (MMRV) vaccine compared to the separate vaccines for MMR and varicella (MMR+V).

"Parents should be informed about the benefits and risks of the combination vaccine," Shannon MacDonald, of the University of Calgary in Alberta, Canada, noted in email to Reuters Health.

"Many parents are concerned about the number of needles that children get at their immunization visits, so this vaccine allows them to reduce two needles down to one. The trade off is a slightly increased (but still very small) risk of febrile seizures," she said.

Dr. MacDonald and colleagues took at look back at data on 227,774 children one to two years old who received either the combined MMRV vaccine (Priorix-Tetra, Glaxo) or the separate MMR+V vaccines between 2006 and 2012 in Alberta, Canada.

In a report online today in CMAJ, they say the risk of seizures seven to 10 days post-vaccination was twice as high with MMRV as with MMR+V (relative risk 1.99; 95% CI 1.30 - 3.05). But the excess absolute risk of seizures with MMRV is still relatively small - 3.52 per 10,000 doses administered, or one excess seizure for every 2841 doses given.

In an interview with Reuters Health, Dr. Nicola P. Klein, co-director of the Vaccine Study Center and research scientist in the Division of Research at Kaiser Permanente Northern California in Oakland, said the findings from Canada are in line with what's been seen in the US, the difference being they used the GlaxoSmithKline vaccine (Priorix-Tetra) where the US exclusively uses the Merck vaccine (ProQuad).

The Canada study found a two-fold increased risk for the combination vaccine seven to 10 days after vaccination in one- to two-year-olds versus the separate vaccines, "which is precisely what we found." The similar findings "really speak to this probably being a class effect and not limited to one manufacturer's vaccine," Dr. Klein said.

"Whether this increase is of practical significance is uncertain," Dr. MacDonald and colleagues note in their paper.

"It is a matter for debate whether the choice of separate versus combination vaccine is a policy decision or a choice for parents to make in consultation with their vaccination provider," they add.

Dr. MacDonald told Reuters Heath, "Although febrile seizures can be frightening for parents, febrile seizures after a vaccine end on their own and don't have any long term health effects. A critical part of the message to parents is that, although the vaccine has a slightly higher risk of febrile seizures compared to the previously separate vaccines, the risk of seizures is significantly higher if the child contracts measles disease (in fact, 10 fold higher). This is in addition to all the other risks from the diseases that the vaccine protects against, including ear infection, pneumonia, brain swelling, infertility, deafness, necrotizing fasciitis, and death."

SOURCE: https://bit.ly/1liK9aZ

CMAJ 2014.

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