(RxWiki News) One of the side effects that a child may experience after receiving a vaccination is fever. In very rare cases, a high fever can lead to a frightening but non-harmful seizure.
The risk of these fever-caused (febrile) seizures is very low, but a recent study found that a child's age when receiving the measles vaccine might affect that risk.
The study found that children who received the vaccine between 16 and 23 months of age were twice as likely to have had a fever-caused seizure than children who were vaccinated between 12 and 15 months.
However, the overall risk of these seizures was still less than 10 in 10,000 children.
Currently, the Centers for Disease Control and Prevention (CDC) recommends that a child receive his or her first dose of the measles vaccine between 12 and 18 months. The CDC recommends the second dose between 4 and 6 years old.
"Follow the CDC immunization schedule recommendations."
The study, led by Ali Rowhani-Rahbar, MD, MPH, PhD, of the Department of Epidemiology at the University of Washington, aimed to find out whether the risk of a fever with a seizure was greater with measles vaccines based on the age at which a child was vaccinated.
The researchers examined the records of 840,348 children, aged 12 months to 23 months old, who received a measles vaccine between 2001 and 2011.
All the children were participating in one of eight sites connected to the Vaccine Safety Datalink — a system that tracks medical information about vaccinated children to use in research.
The researchers looked at the ages when the children received their vaccines and how many children developed a high fever that led to a seizure in the 42 days after being vaccinated.
"Febrile seizures," or seizures caused by a high fever, do not cause any long-term damage to a child.
The two types of vaccines that the children would have received were either the MMR (measles, mumps and rubella) or the combined MMRV (measles, mumps, rubella and varicella, or chickenpox).
The researchers found that children aged 16 to 23 months were 6.5 times more likely to have a fever-caused seizure in the 7 to 10 days after vaccination than during days 11 to 42 after vaccination.
Meanwhile, children receiving the vaccine between 12 and 15 months old were 3.4 times more likely to have a fever-caused seizure in the week and a half after vaccination than they were in the subsequent month.
These risk increases sound high, but a fever-caused seizure is already fairly rare among children being vaccinated against the measles.
For every 10,000 doses of the measles vaccine given, 9.5 children would experience a fever-caused seizure if they received the shot at 16 to 23 months.
Meanwhile, four children out of every 10,000 would experience a fever-caused seizure if they received a measles vaccine between 12 and 15 months.
These findings also mean that children receiving the vaccine between 16 and 23 months were twice as likely to have a fever-caused seizure as children getting the vaccine between 12 and 15 months.
In comparing the two different types of vaccines, the MMRV was 1.4 times more likely to cause a fever than giving the MMR with the varicella (chickenpox) vaccine in separate doses but at the same visits.
The MMRV was twice as likely to lead to a febrile seizure than the MMR by itself, without the varicella vaccine.
Children receiving the MMRV were also twice as likely to experience a fever-caused seizure than children receiving the MMR and the varicella vaccines separately.
The study was published October 14 in the journal JAMA Pediatrics. The research was funded by the US Centers for Disease Control and Prevention through America's Health Insurance Plans.
One author has received research funding from GlaxoSmithKline, one has received research funding from Merck & Co., and one has received it from MedImmune.
Three other authors have received research funding from three or more of the following: Novartis, Pfizer, Sanofi-Pasteur, Merck & Co and GlaxoSmithKline.
The other authors have only received funding from the CDC or National Institutes of Health.