Many parents struggle with whether vaccines, especially multiple vaccines given on the standard schedule, are truly safe. Some parents decide that it may be safer to give vaccinations on a delayed schedule, rather than giving up to 5 immunizations in one visit. A new study, published in the journal Pediatrics, sheds some light on this anxiety provoking subject.
The study examined more than 300,000 children in the US Vaccine Safety Datalink, born between 2004 and 2008. Researchers compared the timing of a first seizure with when each of several vaccine series were begun.
While some parents might assume that an older child could tolerate an immunization with fewer side effects, researchers in this study found that the rate of seizures following vaccination with the MMR (measles-mumps-rubella) vaccine was more than doubled (from 2.65% to 6.53%) in toddlers receiving their first vaccine after the age of 12-15 months versus 16-23 months. They also found that the the rate of seizures was increased in children who delayed the MMRV (measles-mumps-rubella-varicella) vaccine beyond 15 months of age, with a seizure rate of 4.95% to 8.0%.
Some weaknesses of this study are that it did not separate out febrile seizures from epilepsy. Febrile seizures are scary at the time, but generally do not lead to any long term disability. It is well known that vaccines can cause fevers and that high fevers can bring on febrile seizures.
Also, this study did not separate out the risk for seizures based on age alone. Children are at their highest risk for febrile seizures from 16-23 months, so the increased risk of seizure following immunization could be due to this age associated risk alone. This is what a previous study based on a similar group of children found in another recently published study.
The study also was not able to determine the cause of the immunization delay. It is possible that less healthy children were more likely to receive immunizations on a delayed schedule. If this were the case, then the delayed vaccine would not necessarily be the cause of the seizures.
Still, this study does contribute to data suggesting that the standard vaccination schedule for MMR is likely to be at least as safe as the delayed one, if not safer.
Demicheli, Vittorio, Alessandro Rivetti, Maria Grazia Debalini, and Carlo Di Pietrantonj. “Vaccines for Measles, Mumps and Rubella in Children.”Evidence-Based Child Health: A Cochrane Review Journal 8.6 (2013): 2076-238. Web.