Delayed receipt of measles-mumps-rubella and measles-mumps-rubella-varicella vaccines during the second year of life increases the risk for seizures, according to study findings in Pediatrics.
Simon J. Hambidge, MD, PhD, of Kaiser Permanente in Denver, and colleagues reviewed data from the Vaccine Safety Datalink, a collaborative project between the CDC and several managed care organizations across the United States, from 2004 to 2010. Researchers focused on children aged 2 to 24 months.
Of the 5,667 children included in the study, 49.7% were vaccinated on time for all vaccines during their first 2 years of life. Of children who had their first seizure at age 38 to 364 days, 71.2% were vaccinated on time. Sixty-two percent of children who had their first seizure at age 1 to 2 years were vaccinated on time.
There was no association between vaccination and seizures among children vaccinated at the age of 38 to 92 days, as recommended by the Advisory Committee on Immunization Practices. Seizures were less common in this age group overall. The incident rate ratio (IRR) for seizure occurring within 2 days of diphtheria-tetanus-acellular pertussis vaccination compared with control periods was 1.26 (95% CI, 0.65-2.45) for this age group. For children whose first vaccination was delayed between 93 days and 2 years, the IRRs for seizures were higher but insignificant; IRR for DTaP was 1.56 (95% CI, 0.19-12.92).
The researchers also reported that there was an increased risk for seizures 7 to 10 days after vaccination when the MMR vaccine (M-M-R II, Merck) was administered at the ACIP-recommended age of 12 to 15 months. The IRR was 2.65 (95% CI, 1.99-3.55). The risk for seizures increased if the MMR vaccine was received later than age 15 months, with IRR of 6.53 (95% CI, 3.15-13.53). Receipt of MMR vaccine at 16 to 18 months had an IRR of 5.09 (95% CI, 2.05-12.66). The risk for seizure after MMR vaccination was most prominent in children who received the vaccine at 19 to 21 months, with an IRR of 8.75 (95% CI, 2.35-32.58).
The MMRV vaccine (ProQuad, Merck) was associated with an increased risk for seizures 7 to 10 days after vaccination. When received at 12 to 15 months, the IRR was 2.75 (95% CI, 2.03-3.7). Risk increased with age; the IRR for seizures was 3.64 when vaccinated at 16 to 23 months, according to the study findings.
The association between vaccination and seizure was twice as high for recipients of MMRV than recipients of MMR vaccine, regardless of those who were vaccinated on time or delayed.
“Given the overall low absolute risk of seizures after MMR and MMRV vaccines, the lack of association of simple febrile seizures with long-term adverse consequences, and the known benefits of on-time vaccination, our findings provide additional rationale for not delaying childhood vaccinations,” the researchers concluded.
Disclosure: The researchers report no relevant financial disclosures.