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MMR vaccine associated with heightened risk for ITP

O’Leary ST. Pediatrics 2012;doi:10.1542/peds.2011-1111.

Routine childhood vaccines given in the first year of life were not associated with increased risk for immune thrombocytopenic purpura, but measles-mumps-rubella vaccines administered at 12 to 19 months demonstrated a significant association, according to study results published online.

Using the medical records of five managed care organizations from 2000 to 2009, Sean T. O’Leary, MD, MPH, and colleagues analyzed the risk for immune thrombocytopenic purpura (ITP) in children aged 6 weeks to 18 years after all routine childhood vaccines were administered, as well as the risk for serious complications of ITP after vaccination in children.

Researchers identified a cohort of 1.8 million eligible children by using electronic databases. The data were reviewed to exclude cases of thrombocytopenia from other known conditions by using the ICD-9 diagnosis codes — including acquired hemolytic anemia, aplastic anemia, neonatal thrombocytopenia, disseminated intravascular coagulation, chronic liver disease or malignancy.

The researchers further classified children aged younger than 18 years with either two platelet counts of less than 50,000/mcL in a 6-week period or one platelet count of less than 50,000/mcL with an associated ICD-9 code between 287 and 287.9 within 6 weeks of the low platelet count.

At the conclusion of the study, 197 children were diagnosed with ITP. According to the findings, none of the routine childhood vaccines given in the first year of life was significantly associated with heightened risk for ITP. However, for vaccines routinely administered at 12 to 19 months of age, there was a significant association of ITP with MMR (IRR=5.48; 95% CI, 1.61-18.64).

Researchers also examined other vaccines commonly given during this age range and found an association of increased risk for ITP with hepatitis A vaccine, varicella vaccine and diphtheria-tetanus-acellular pertussis vaccine in children older than 6 years.

Disclosure: The researchers report no relevant financial disclosures.

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