Delayed Vaccination Schedule Poses Seizure Risk

Citing a crowded immunization schedule and fearfulness of vaccinations, many families choose to delay the administration of early childhood vaccines, adhering instead to alternative, untested, delayed immunization schedules. Delayed schedules contribute to disease outbreaks by increasing the time children are unprotected from vaccine-preventable diseases and might increase the risk for postvaccination seizures.

To examine the association between delayed first dose of measles-mumps-rubella (MMR) vaccine administration and first occurrence of postvaccination seizure (7–10 days after vaccination) in children aged ≤2 years, researchers analyzed data from a cohort study of 300,000 children born in the U.S. between 2004 and 2008. The study group comprised 5667 children who developed seizures between ages 38 and 730 days. Approximately one third of children had a delayed vaccination schedule (28% of those with seizure in the first year and 38% of those with seizure in the second year).

Timing of first MMR vaccine dose was not associated with increased risk for postvaccination seizures in infants but was increased in children vaccinated between ages 16 and 23 months (incidence rate ratio, 6.53 for vaccine administration at 16–23 months vs. 2.65 at <16 months). The risk was further increased in children vaccinated between ages 19 and 23 months (IRR, 8.75) and highest for measles-mumps-rubella-varicella vaccination at age >15 months (IRR, 9.8).