Published online February 29, 2008
PEDIATRICS Vol. 121 No. 3 March 2008, pp. e687-e692 (doi:10.1542/peds.2007-1578)
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ARTICLE

Risk of Immune Thrombocytopenic Purpura After Measles-Mumps-Rubella Immunization in Children

Eric K. France, MD, MSPHa, Jason Glanz, PhDb, Stanley Xu, PhDb, Simon Hambidge, MD, PhDb, Kristi Yamasaki, PharmDb, Steve B. Black, MDc, Michael Marcy, MDd, John P. Mullooly, PhDe, Lisa A. Jackson, MD, MPHf, James Nordin, MDg, Edward A. Belongia, MDh, K. Hohman, MPHi, Robert T. Chen, MDj, Robert Davis, MD, MPHk for the Vaccine Safety Datalink Team

a Department of Preventive Medicine
b Clinical Research Unit, Kaiser Permanente Colorado, Denver, Colorado
c Kaiser Permanente Vaccine Study Center, Kaiser Permanente Northern California, Oakland, California
d Center for Vaccine Research, Kaiser Permanente Southern California, Torrance, California
e Center for Health Research, Kaiser Permanente Northwest, Portland, Oregon
f Group Health Cooperative, Group Health Center for Health Studies, Seattle, Washington
g Department of Vaccine Research, HealthPartners Research Foundation, Minneapolis, Minnesota
h Epidemiology Research Center, Marshfield Clinic Research Foundation, Marshfield, Wisconsin
i Department of Ambulatory Care and Prevention, Harvard Pilgrim Health Care, Boston, Massachusetts
j Division of HIV/AIDS Prevention
k Immunization Safety Office, Centers for Disease Control and Prevention (CDC), Atlanta, Georgia

BACKGROUND. The measles-mumps-rubella vaccine has been associated with immune thrombocytopenia purpura in 2 small studies.

METHODS. By using the Vaccine Safety Datalink, we identified measles-mumps-rubella–vaccinated children aged 1 to 18. A case of immune thrombocytopenia purpura was defined as a patient with a platelet count of ≤50000/µL with clinical bleeding and normal red and white blood cell indices. The immune thrombocytopenia purpura incidence rates during exposed (42 days after vaccination) and unexposed time periods were determined. A retrospective cohort of vaccinated children was used to determine incident rate ratios for children aged 1 to 18 years, 12 to 23 months, and 12 to 15 months.

RESULTS. A total of 1036689 children received 1107814 measles-mumps-rubella vaccinations; there were 259 confirmed patients with immune thrombocytopenia purpura. Because only 5 exposed cases occurred after age 2, analyses were limited to children aged 12 to 23 months. Exposed patients aged 12 to 23 months had lower median platelet counts than those who were unexposed and had similar median duration of illness (11 vs 10 days). The incident rate ratio was highest for children aged 12 to 15 months at 7.10. The incident rate ratio for boys aged 12 to 15 months was 14.59, and the incident rate ratio for girls in the same age group was 3.22. Seventy-six percent of immune thrombocytopenia purpura cases in children aged 12 to 23 months were attributable to measles-mumps-rubella vaccination. This vaccine causes 1 case of immune thrombocytopenia purpura per every 40000 doses.

CONCLUSION. Measles-mumps-rubella vaccine that is given in the second year of life is associated with an increased risk of immune thrombocytopenia purpura.

Key Words: immune thrombocytopenia purpura • children • measles-mumps-rubella vaccines • thrombocytopenia

Abbreviations: MMR—measles-mumps-rubella • ITP—immune thrombocytopenic purpura • IRR—incident rate ratio • CI—confidence interval • VSD—Vaccine Safety Datalink • CDC— Centers for Disease Control and Prevention • MCO—managed care organization • ICD-9—International Classification of Diseases, Ninth Revision • SCCS—self-controlled case series

Accepted Nov 30, 2007.