HealthDay News — An acellular-pertussis combination vaccine that also protects against diptheria, tetanus, poliovirus and Haemophilus influenza type b is associated with a small increased risk for febrile seizures after the first and second doses of the four-dose vaccine series — less than four per 100,000 vaccinations, data indicates.
“The relative risks of febrile seizures were increased on the day of the first and the second vaccinations, but the absolute risks were low,” Yuelian Sun, PhD, of Aarhus University in Denmark, and colleagues reported in the Journal of the American Medical Association.
Although previous studies have shown that vaccines containing whole-cell pertussis increase the risk for seizures, whether the risk applied to acellular-pertussis formulations was unknown.
So Sun and colleagues, examined the risk for seizures and epilepsy with the combined diphtheria-tetanus toxoids-acellular pertussis-inactivated poliovirus-Haemophilus influenza type b (DTaP-IPV-Hib) vaccine in a population-based cohort study involving 378,834 Danish children born from 2003 to 2008. Follow up was conducted through 2009.
In Denmark DTaP-IPV-Hib vaccine is available free of charge from general practitioners, who are reimbursed by the Public Health System. The recommended vaccination schedule consists of vaccines administered at ages 3, 5 and 12 months, with a booster at 5 years. Data from national registries indicated that a total of 329,521 children were exposed to the first vaccination; 339,288 to the second; and 339,288 to the third; whereas, 6,854 (1.8%) children did not receive any DTaP-IPV-Hib vaccines.
Before 18 months of age, a total of 7,811 children (2.1%) were diagnosed with febrile seizures. Among those diagnosed: 17 experienced a febrile seizure in the zero to seven days after the first dose (incident rate: 0.8 per 100,000 person days); 32 in the week after the second dose (IR: 1.3 per 100,000 person days); and 201 in the week after the third vaccination (IR: 8.5 per 100,000 person days).
Compared with a reference cohort of children who experienced seizures outside of the zero to seven day window after vaccination, the researchers found no overall increased risk of febrile seizures during the zero to seven days after the three vaccinations. An increased risk of febrile seizures was identified on the day of the first and second vaccinations (hazard ratios= 6.02 and 3.94, respectively), but not on the day of the third vaccination (HR= 1.07).
On the day of vaccination, nine, 12 and 27 children were diagnosed with febrile seizures after the first, second and third vaccinations, respectively (corresponding IRs: 5.5, 5.7 and 13.1 per 100,000 person-days).
“Although the relative risks of febrile seizures on the day of the two DTaP-IPV-Hib vaccinations were increased, the absolute risk of febrile seizures after DTaP-IPV-Hib vaccination was very low, and the prognosis of febrile seizures occurring shortly after vaccination was similar to the prognosis of febrile seizures occurring outside the risk period of vaccination,” the researchers wrote.
No association was found between DTaP-IPV-Hib vaccination and epilepsy.