A Link Between Acellular Pertussis Combination Vaccine and Risk of Febrile Seizures?
The risk of febrile seizures increases on the day of the first and second, but not third, administration of diphtheria-tetanus-acellular pertussis–inactivated poliovirus–Haemophilus influenzae type b (DTaP–IPV–Hib) vaccine, according to research published in the February 22/29 issue of JAMA. The overall risk of febrile seizures is less than four per 100,000 vaccinations, however, and the risk does not increase within seven days of vaccination.
Investigators had previously found that vaccination with whole-cell pertussis vaccine increases the risk of febrile seizures. Acellular pertussis vaccine has been included in the DTaP–IPV–Hib vaccine since 2002 in Denmark. Yuelian Sun, PhD, of the Department of Public Health at Aarhus University in Denmark, conducted a population-based cohort study to determine whether acellular pertussis vaccine increased the risk of febrile seizures and epilepsy.
She and her colleagues selected 378,834 children born in Denmark between January 1, 2003, and December 31, 2008. The children were followed up through December 31, 2009. During follow-up, researchers conducted a self-controlled case series (SCCS) study analysis on children with febrile seizures. The main outcome measures of the cohort study were the hazard ratio (HR) of febrile seizures within zero to seven days after each vaccination and HR of epilepsy after the first vaccination. Relative incidence of febrile seizures within zero to seven days after each vaccination was the main outcome measure in the SCCS study.
At 18 months of follow-up, 7,811 children were diagnosed with febrile seizures. Of these children, 17 were diagnosed within seven days of the first vaccination, 32 children after the second vaccination, and 201 children after the third vaccination. Children did not have a higher risk of febrile seizures during the seven days after the three vaccinations.
On the day of vaccination, nine children were diagnosed with febrile seizures after the first, 12 children were diagnosed after the second, and 27 children were diagnosed after the third vaccination. The results of the SCCS study were similar to those of the cohort study.
Within seven years of follow-up, 131 unvaccinated children and 2,117 vaccinated children were diagnosed with epilepsy. Children had a lower risk of epilepsy between three and 15 months after vaccination, and a similar risk of epilepsy later in life to that of unvaccinated children.
“It is unclear why the HRs of febrile seizure increased only after the first two vaccinations, but not after the third vaccination when the underlying incidence of febrile seizures was higher,” said Dr. Sun. “There may be more competing risk factors for febrile seizures during a period in which the incidence of febrile seizures is high and the relative importance of a single risk factor like vaccination may be lower,” she concluded.
Sun Y, Christensen J, Hviid A, et al. Risk of febrile seizures and epilepsy after vaccination with diphtheria, tetanus, acellular pertussis, inactivated poliovirus, and Haemophilus influenzae type b. JAMA. 2012;307(8):823-831.
Deep-Brain Stimulation Improves Memory of Spatial Information
Stimulating the entorhinal region of a patient’s brain while he or she is learning spatial information enhances the patient’s memory of that information, according to a study published in the February 9 issue of the New England Journal of Medicine.
Nanthia Suthana, PhD, a postdoctoral researcher at the David Geffen School of Medicine in Los Angeles, and her colleagues applied deep-brain stimulation to the hippocampal and entorhinal regions of patients’ brains at levels that do not elicit an afterdischarge (ie, a neuronal discharge that occurs after the stimulus ends). The group studied seven patients with drug-resistant epilepsy who had received implantation of intracranial depth electrodes for seven to 10 days to determine the area of seizure onset. Six patients had entorhinal electrodes, and five had at least one hippocampal electrode.
All patients completed a spatial learning task that required them to navigate through a virtual environment to deliver passengers to six locations. The investigators applied stimulation of 1.0 to 2.0 mA while patients were learning certain locations, but not while they were learning other locations. Stimulation was applied consistently with regard to location. Consecutive trials alternated between stimulation and nonstimulation for each patient.
Patients took more direct routes to locations that they had learned while receiving stimulation of the entorhinal region and less time to deliver passengers to those locations than they did for locations that they had learned without receiving stimulation. Memory performance improved in all participants who had received entorhinal stimulation. Stimulation of the hippocampus, however, had no effect on whether patients took a more direct path, or on how long they took to deliver passengers.