Investigating a potential link between MMR vaccine and immune thrombocytopenia purpura.
Investigators designed a large-scale study to evaluate what two small studies with considerable limitations already have shown-that the measles-mumps-rubella (MMR) vaccine is associated with an increased risk of immune thrombocytopenia purpura (ITP).
Using Centers for Disease Control and Prevention data, researchers identified MMR-vaccinated children from 1 to 18 years of age. They then determined ITP incidence rates in these children during "exposed" (42 days after vaccination) and "unexposed" time periods.
Of more than 1 million children who received the vaccinations, 259 had confirmed ITP. ITP was defined as a platelet count of ≤50,000/μL with normal red and white blood cell indices, the presence of clinical signs and symptoms of spontaneous bleeding, and absence of fever. Most (80%) of the MMR-exposed ITP cases were in children between 12 and 23 months old.
This finding is not surprising, given the association between wild measles and ITP. While many cases of ITP in this age range may be due to MMR, it is still a rare complication (one in 40,000 doses). This is not a reason to avoid administering MMR. It is a reminder, however, that we need to be the experts on vaccine safety for our patients and their parents. Misinformation is abundant. For clear evidence-based information on what is and what is not a complication of vaccinations, visit the Institute for Vaccine Safety at http://www.vaccinesafety.edu/.