Although the combined vaccine against measles, mumps and chickenpox comes with a small risk of fever-related seizures in toddlers, a new study suggests that's not true in older children.
The measles-mumps-rubella-varicella (MMRV) vaccine has been available in the U.S. since 2005. It combines the traditional MMR vaccine with the anti-chickenpox shot so young children can undergo fewer jabs.
But after its release, the MMRV vaccine was found to carry a small risk of fever-related seizures in one- to two-year-olds -- the age at which the first dose of the vaccine is given.
Fever-related, or "febrile," seizures are short-lived, lasting about a minute or two.
Though the seizures are "very scary" for parents, "they are not dangerous, and they do not lead to later epilepsy or seizure disorders," lead researcher Dr. Nicola Klein, co-director of the Kaiser Permanente Vaccine Study Center in Oakland, California, told Reuters Health in an email.
Experts now recommend that parents opt for either the MMRV or separate MMR and varicella shots for their toddlers. The separate shots seem to cut the odds of a fever-related seizure.
But that has still left questions about the second MMRV vaccine, which is given between the ages of four and six.
In the new study, researchers found no evidence that the vaccine significantly raised the risk of fever-related seizures in those older children.
The findings, reported in the journal Pediatrics, are based on medical records for nearly 87,000 four- to six-year-olds who received the MMRV shot between 2006 and 2008. Another 67,000-plus received the MMR and varicella vaccines separately, on the same day, between 2000 and 2008.
One child had a fever-related seizure seven to 10 days after getting the MMRV vaccine -- the time frame in which one- to two-year-olds appear to be at risk. No seizures were recorded in kids who had the MMR and varicella shots separately.
The findings suggest the vaccine carries no particular risk of the seizures in older kids. Fever-related seizures are fairly common in children; according to the National Institutes of Health, about one in every 25 kids will have at least one fever-related seizure -- though they most often affect toddlers.
So it's not surprising that the MMRV shot has been linked to seizures in toddlers, but not in older kids, according to Klein's team.
Even in toddlers, the risk is small, said Klein.
"It is more common for a child to have a febrile seizure caused by a cold than by an immunization," she said.
In a 2010 study, Klein's team found that compared with one- to two-year-olds who got separate MMR and varicella jabs, those given the combined vaccine had twice the rate of fever-related seizures seven to 10 days later.
That translated to one additional seizure for every 2,300 doses of the MMRV shot given to one-year-olds instead of the separate vaccines.
Klein said that parents should talk with their pediatrician about the pros and cons of the MMRV vaccine versus giving toddlers the MMR and varicella vaccines separately.
The vaccine is not the only one that's associated with fever-related seizures in very young children. A recent study found a small risk among babies getting the combined vaccine against diphtheria, tetanus, whooping cough (pertussis), polio and Haemophilus influenzae type 2 -- known collectively as DTap-IPV-Hib (see Reuters Health story of February 21, 2012).
But again, experts stressed that the risk was "very small" and the vaccine was not linked to future seizure disorders.
Klein and some of her co-researchers on the study have received past research funding from vaccine makers, including Merck, which makes the ProQuad MMRV vaccine.