Pertussis vaccination might trigger earlier onset of seizures in children with the genetic disorder Dravet syndrome, but does not worsen the condition or the intellectual disability that many of these patients experience, a retrospective study published online in the June edition of The Lancet Neurology reports. The article concludes that the vaccination should not be withheld from children with Dravet syndrome because vaccination before or after disease onset does not affect their clinical outlook. 

Proposed links between childhood vaccination and neurological disorders have repeatedly caused controversy and have affected vaccination uptake. Pertussis vaccine—to prevent whooping cough—is routinely given to children together with diphtheria and typhoid vaccines (DTP), has been linked in the past with vaccine encephalopathy—in which seizures and intellectual disability develop. An Australia-wide team led by Samuel Berkovic of the Epilepsy Research Centre at the University of Melbourne reported in The Lancet Neurology in 2006 that 12 of 14 patients with had vaccine-induced brain disease (encephalopathy) and were subsequently found to have Dravet syndrome, which was associated with mutations of the sodium channel gene SCN1A in 11 of the 12 affected children.

To confirm the association between DTP vaccination and Dravet syndrome and determine whether vaccination affects time of onset or clinical outcome of the disorder, Anne McIntosh and Jacinta McMahon (Epilepsy Research Centre, University of Melbourne, Victoria) and colleagues, led by Berkovic and Ingrid Scheffer, retrospectively studied 40 patients with Dravet syndrome. The group was selected because they had mutations in SCN1A, a first seizure that was a convulsion, and validated medical and vaccination records, and not because of any temporal link of seizures with vaccination.

The team found a peak in the number of patients who had seizure onset within 2 days of vaccination. So the authors separated the children into two groups according to whether seizure onset occurred on the day or day after vaccination, or not. 

The average age at seizure onset was significantly lower in the vaccination-proximate group (18 weeks) compared with the vaccination-distant group (26 weeks). There were no differences in intellectual outcome, subsequent seizure type, or gene mutation type between the two groups. A further analysis found that intellectual outcome did not differ between patients who received vaccinations after seizure onset and those who did not.

Universal vaccination in infancy is a controversial issue, in which science, societal views and social policy are sometimes poorly aligned,” say the authors, paraphrasing a recent authoritative review by Professors Simon Shorvon (UK) and Anne Berg (USA).  The article authors compare the attention given to the previous debate over pertussis vaccination and so-called vaccine encephalopathy to that given recently to the debate over MMR vaccine and autism.

“Vaccination might trigger earlier onset of Dravet syndrome in children who, because of an SCN1A mutation, are destined to develop the disease,” the authors note. “However, vaccination should not be withheld from children with SCN1A mutations because we found no evidence that vaccinations before or after disease onset affect outcome.”

In a comment, Max Wiznitzer from the Rainbow Babies & Children’s Hospital in Cleveland notes that the study is “consistent with the conclusion that outcome is determined by the underlying disorder and not by proximity to vaccine administration.”  Moreover, he urges: “Through effective and accurate information and communication about benefits and realistic risks, public confidence in vaccines can be strengthened.”

Note: Immunization of infants and children saves lives by preventing diseases which can be serious in some children. Immunizations, however, may produce fever in some infants, and the group with the gene abnormaility associated with Dravet syndrome may have their first seizure(s) at that time. Any fever may lead to these initial events in these children, but because the "baby shots" are given at that age, there seemed to be a link. The immunization is not the cause of Dravet, rather just a precipitant.

This research should allow parents to appropriately proceed with immunizing their infants as recommended. --Epilepsy Foundation Professional Advisory Board member, John M.Pellock, M.D., Professor and Chairman, Division of Child Neurology Virginia Commonwealth University

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