(NaturalNews) Confirming the results of prior studies, research conducted by the University of Calgary and published in the Canadian Medical Association Journal has found that the combination MMR-chickenpox vaccine doubles the risk of febrile seizures in young children.
The researchers reviewed side effect data from 277,774 children who had received either the combined MMRV (measles-mumps-rubella-varicella) vaccine or two separate vaccines (MMR and varicella/chickenpox) between the ages of 12 and 23 months.
The researchers found that, among children who received the vaccines separately, less than 0.2 per 1,000 experienced febrile seizure -- fever-induced convulsions that infants and young children are particularly susceptible to. Among children who had received the MMRV vaccine, however, the febrile seizure rate went up to 0.352 per 1,000.
Seizure evidence mounts
Studies conducted in the United States have found a similar increase in febrile seizure risk with the MMRV vaccine, compared with separate MMR and chickenpox vaccines. It was these findings that led the US Advisory Committee on Immunization Practices to suggest that the first dose of each vaccine be given separately at around age 12 months. The Advisory Committee maintained its recommendation that the combined vaccine be given later on, however, when the risk of febrile seizures is believed to decrease.
US studies have found even higher rates of seizures than those in the Canadian study, however. According to the US Centers for Disease Control and Prevention (CDC), the MMR vaccine alone causes febrile seizures in about 1 out of every 3,000 cases, or 0.33 per 1,000.
Likewise, a 2006 study found that, within five to 12 days of vaccination, the rate of febrile seizure among children separately given MMR and varicella vaccines on the same doctor visit was 0.2 per 1,000. In contrast, children given Merck's MMRV vaccine ProQuad had a 0.5 per 1,000 rate of febrile seizure (1 in 2,500).
Notably, the febrile seizure rates for both the MMRV vaccine and the separate MMR and varicella vaccines given on the same day climbed to 1.3 per 1,000 (one in 770) when researchers looked at the period spanning 30 days after the vaccination(s).
A later CDC study found a 0.4 per 1,000 febrile seizure rate within seven to 10 days among children given separate vaccines, and a 0.9 per 1,000 seizure rate among children given MMRV -- in this case, more than doubling the risk.
Study may produce policy changes
Nine of Canada's 13 provinces routinely administer the combined MMRV shot as part of the standard childhood vaccination schedule, starting at a very young age. In a policy more similar to that followed in the United States, the province of Ontario gives the MMR and varicella vaccine separately for the first dose, then switches over to the combined shot for the second dose sometime between four and six years of age. Likewise, British Columbia does not give the combined vaccine to babies, but it will begin administering the combined vaccine to older children starting in July.
Many public health officials cite parental concerns over vaccination as the primary reasons for adopting the combined vaccine: parents who are skittish about potential side effects of vaccines or about the unpleasantness of shots for their children are more likely to complete an entire schedule that contains fewer shots.
Yet, increased risk of a potentially serious side effect may have the opposite effect.
When children experience seizures following vaccination, said lead researcher Dr. Shannon MacDonald, it "may undermine confidence in immunization programs."
Although often harmless, some febrile seizures may be caused by inflammation within the brain. For this reason, Dr. Robert Sears, author of The Vaccine Book, recommends that children who have experienced this vaccine reaction once not be given the same vaccine again.