A new study has found that children who get a combination vaccine have a slightly higher risk of having a fever-induced seizure than children who got two vaccinations to protect against the same diseases.
The vaccine is the combined measles, mumps, rubella and chickenpox shot, which was developed to cut back on the number of vaccinations children get early in life.
Alberta researchers say kids who got their first dose of the combined shot between 12 and 23 months had double the risk of having a seizure than those who got a measles, mumps and rubella shot in one arm and a chickenpox shot in the other.
While the risk is double, it is still small.
The study suggests between three and four more children per 10,000 kids who get the combined shot will end up seeing a doctor or going to a hospital emergency room because of a febrile seizure (a seizure brought on by fever).
The study is published today in the Canadian Medical Association Journal. The lead author is Doctor Shannon MacDonald, a nurse and a post-doctoral fellow in the University of Calgary's faculty of medicine.
MacDonald says it is important to monitor vaccine safety and to inform parents of any detected adverse side-effects. But she says the risks from the diseases this vaccine protects against remain much higher than the side-effects occasionally reported after its use.
"So it's an important finding but it's not a reason for somebody to not vaccinate their child," says MacDonald.
"It's a very small number. And … the risk of febrile seizures from measles disease is very high. It's 60 to 70 seizures per 10,000 children, compared to what we were talking about, which was an increased risk of three per 10,000."
As well, an average of one in 1,000 children who contract measles will suffer swelling of the brain and about one in 1,000 die from measles, MacDonald says.
The findings are in keeping with those of research done elsewhere, says Dr. Kumanan Wilson, senior scientist at the Ottawa Health Research Institute.
He says parents should be alerted to the increased risk, especially as these seizures typically happen seven to 10 days after a child gets the shot. If parents aren't warned of the possibility, they may not expect a side-effect to develop such a long time after the vaccination. It could be unsettling for parents, Wilson says.
MacDonald agrees, saying parents should be told to be on the lookout for fever and treat it promptly if the child develops a temperature.
The researchers looked at nearly 277,000 children in Alberta who were vaccinated against measles, mumps, rubella and varicella – the virus that causes chickenpox – between 2006 and 2012.
Alberta introduced the combined vaccine in 2010.
MacDonald and her co-authors looked at rates of febrile seizures in the children who received separate vaccines for measles, mumps and rubella (one shot) and varicella from 2006 to 2009, and compared those rates to the experience seen after the combined vaccine was put into use.
Nine of Canada's 13 provinces and territories now use the combined measles, mumps, rubella and varicella vaccine, which is made by GlaxoSmithKline. A similar combined vaccine in the United States, made by Merck, has also been linked to increased rates of febrile seizures.
In fact, last December, the World Health Organization's expert committee on vaccinations, which goes by the acronym SAGE (Strategic Advisory Group of Experts on Immunization), published a report noting the increased risk of febrile seizures associated with these combination vaccines.
They said seizures were reported at a rate of seven to nine per 10,000 children who received the four-component vaccine as compared to three to four per 10,000 for children who got a measles, mumps and rubella shot and a separate chickenpox vaccine.
MacDonald says parents may want to discuss with their child's doctor whether the child should be given the combination shot or a separate varicella vaccine.
And Wilson says researchers should look into the cost to the health-care system of this increase in febrile seizures.