the absolute risk of a child developing idiopathic thrombocytopenic purpura (ITP) within 6 weeks of the first MMR vaccine has been found to be 1 in 22,300 cases, with 2/3 of cases being attributable to MMR (1)
there is a much greater risk of developing ITP after "wild" measles (common), rubella (about 1 in 3,000 cases) or mumps (rare) virus infection (1)
the CSM has recommended:
if a child develops ITP within 6 weeks of the first dose of MMR vaccine (or its component vaccines) then there should be evaluation of serological status before the second dose is due. If results of serology testing suggests that the child is not fully immune against measles, mumps and rubella then it is recommended that a second dose of MMR is given - this is because patients not protected by MMR are at risk of ITP from natural infection, in addition to the other complications of measles, mumps and rubella
Notes:
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
in this study the results revealed the vaccine caused 1 case of immune thrombocytopenia purpura per every 40,000 doses
the study authors concluded that MMR given in the second year of life is associated with an increased risk of immune thrombocytopenia purpura
Reference:
(1) CSM/MCA (2001). Current problems in pharmacovigilance, 27, 15.
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