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Vaccine linked to earlier onset of seizures in Dravet syndrome

OnMedica staff

Wednesday, 5 May 2010

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Vaccination should not be withheld from children with Dravet syndrome – even though vaccination is associated with earlier onset of seizures – because clinical outlook is unaffected by vaccination before or after disease onset, say experts in June's The Lancet Neurology and Online First.

The authors of the retrospective study say that although they found that onset of the neurological disorder Dravet syndrome occurred earlier in immunised children, the children were destined to develop the condition anyway, and were no worse off than unvaccinated children in terms of intellectual outcome.

Pertussis vaccine has been linked with vaccine encephalopathy – in which seizures and intellectual disability develop. One study from 2006 found that 12 of 14 patients with so-called vaccine encephalopathy subsequently were found to have Dravet syndrome, which was associated with mutations of the sodium channel gene SCN1A in 11 of the 12 affected children.

The authors of this new study, from Australia, investigated the association between diphtheria-tetanus-pertussis (DTP) vaccination and Dravet syndrome, and whether vaccination affects time of onset or clinical outcome of the disorder. They retrospectively studied 40 patients with Dravet syndrome, who were 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.

There was a peak in the number of patients who had seizure onset within two days of vaccination, so the investigators separated the children into two groups according to whether seizure onset occurred on the day of or day after vaccination (vaccination-proximate group), or later than that (vaccination-distant group).

Seizure onset occurred at a significantly younger age in the vaccination-proximate group (18.4 weeks) compared with the vaccination-distant group (26.2 weeks). But there were no differences in intellectual outcome, subsequent seizure type, or gene mutation type between the two groups. And a further analysis showed that intellectual outcome was similar in patients who received vaccinations after seizure onset and those who did not.

The authors acknowledge the emotive debate around universal vaccination in infancy is an emotive issue, and liken 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,” they say. “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.”

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