OTTAWA — Combining two common childhood vaccines into one — rather than administering them separately — doubles the risk of febrile seizures in children, a study published in the Canadian Medical Association Journal has found.
Febrile seizures, convulsions brought on by fever in infants or young children, are a rare side-effect of measles-mumps-rubella vaccine, occurring at a rate of less than two seizures per 10,000 doses. When the MMR vaccine is combined with the vaccine against chickenpox, creating the MMRV (for varicella) vaccine, that risk doubles. It still remains relatively small, however — at a rate of 3.52 seizures per 10,000 doses, according to the study by a team led by Dr. Shannon MacDonald at the University of Calgary’s faculty of medicine. Seizures among high-risk children were not significantly different, the study also found.
In British Columbia, the doubled MMRV vaccine is not given to babies because of the higher risk of febrile seizures, according to Dr. Monika Naus, the medical director of immunization programs for the B.C. Centre for Disease Control.
In July B.C. will begin administering the MMRV as a second dose to school-aged children who have already had separate vaccines against measles-mumps-rubella and chickenpox. But those children are at no risk because febrile seizures are a factor only in babies, Naus said.
Febrile seizures rarely have long-term effects, MacDonald said, but they do cause distress “and may undermine confidence in immunization programs.”
And that is a big worry.
At a time when measles, which had been eradicated in North America, is seeing a record resurgence, anything with the potential to reduce vaccination rates further is studied carefully by public health officials. A growing anti-vaccine movement has led to pockets of lower vaccination rates across North America.
In fact, the combined measles-mumps-rubella-varicella vaccine was adopted in some regions — although not in Ontario for the first dose children receive — to address waning vaccine rates.
There are good reasons to use the combined vaccine, MacDonald said.
“Combining MMR and varicella into a single vaccine decreases pain for children and distress for parents, thus addressing common barriers to vaccine uptake and may improve vaccination coverage levels and decrease immunization delivery costs.”
Deciding whether to offer separate vaccines or a combination is, ultimately, a policy decision, said MacDonald, whose findings were consistent with a study on the U.S. version of the vaccine.
The U.S. findings led its Advisory Committee on Immunization Practices to withdraw its preference for use of the combination vaccine for the first dose (usually administered to children at about 12 months). The committee advised health officials and parents to discuss the benefits and risks of each option before choosing. If there is no preference, it recommends the separate vaccines be given for the first dose in young children (12-47 months) and the combined vaccine be given to older children or those getting a second dose.
Naus said when the U.S. findings came out the BCCDC chose to not institute a combined vaccine for babies. But it decided in 2012 to administer the combination to children ages 4-6 at the beginning of school starting in 2014.
The findings come as B.C. suffers through a resurgence of measles, particularly in the upper Fraser Valley because of parental resistance to vaccinations.
But Naus said people need to understand their children are more at risk of illness and possibly death from not getting vaccinated.
Parents also need to understand febrile seizures are not dangerous in the long term and children usually outgrow them by the age of two, she said.
“We know that vaccines can cause febrile seizures. Febrile seizures are benign. Children who have febrile seizures with vaccines will have febrile seizures after other triggers like infections, and the important thing is vaccinations prevent those infections so these children are actually better off immunized than getting the real measles, the real chicken pox, which are associated with far greater levels of fever and illness,” Naus said.
The researchers studied data from 277,774 children between 12 and 23 months who received either the combined MMRV vaccine or separate MMR and varicella vaccines. Alberta, where the study was conducted, replaced the separate vaccines with the combined vaccine in 2010. Nine of 13 Canadian provinces and territories administer the combined vaccine as part of their routine childhood immunization schedule. In Ontario, children are given separate vaccines for the first dose and the combined vaccine when they are between four and six years old.
A spokesperson for the Ontario Ministry of Health said it will review the study but that it already recommends separate vaccines for younger ages because of previous studies with similar findings.