The risk of immune thrombocytopenic purpura after vaccination in children and adolescents.
BACKGROUND
The risk of immune thrombocytopenic purpura (ITP) after childhood vaccines other than measles-mumps-rubella vaccine (MMR) is unknown.


METHODS
Using data from 5 managed care organizations for 2000 to 2009, we identified a cohort of 1.8 million children ages 6 weeks to 17 years. Potential ITP cases were identified by using diagnostic codes and platelet counts. All cases were verified by chart review. Incidence rate ratios were calculated comparing the risk of ITP in risk (1 to 42 days after vaccination) and control periods.


RESULTS
There were 197 chart-confirmed ITP cases out of 1.8 million children in the cohort. There was no elevated risk of ITP after any vaccine in early childhood other than MMR in the 12- to 19-month age group. There was a significantly elevated risk of ITP after hepatitis A vaccine at 7 to 17 years of age, and for varicella vaccine and tetanus-diphtheria-acellular pertussis vaccine at 11 to 17 years of age. For hepatitis A, varicella, and tetanus-diphtheria-acellular pertussis vaccines, elevated risks were based on one to two vaccine-exposed cases. Most cases were acute and mild with no long-term sequelae.


CONCLUSIONS
ITP is unlikely after early childhood vaccines other than MMR. Because of the small number of exposed cases and potential confounding, the possible association of ITP with hepatitis A, varicella, and tetanus-diphtheria-acellular pertussis vaccines in older children requires further investigation.
Department of Pediatrics, University of Colorado Anschutz Medical Campus, Aurora, CO, USA. sean.o'leary@childrenscolorado.org
Sean T
ST
O'Leary
Jason M
JM
Glanz
David L
DL
McClure
Aysha
A
Akhtar
Matthew F
MF
Daley
Cynthia
C
Nakasato
Roger
R
Baxter
Robert L
RL
Davis
Hector S
HS
Izurieta
Tracy A
TA
Lieu
Robert
R
Ball
D000293:Adolescent; D019433:Chickenpox Vaccine / Q000009:adverse effects / Q000276:immunology; D002648:Child; D002675:Child, Preschool; D015331:Cohort Studies; D022681:Diphtheria-Tetanus-acellular Pertussis Vaccines / Q000009:adverse effects / Q000276:immunology; D005260:Female; D022362:Hepatitis A Vaccines / Q000009:adverse effects / Q000276:immunology; D006801:Humans; D007223:Infant; D008297:Male; D016553:Purpura, Thrombocytopenic, Idiopathic / Q000453:epidemiology* / Q000209:etiology*; D012189:Retrospective Studies; D012306:Risk; D014481:United States; D014611:Vaccination / Q000009:adverse effects*
D019433:Chickenpox Vaccine; D022681:Diphtheria-Tetanus-acellular Pertussis Vaccines; D022362:Hepatitis A Vaccines