Study: Does the MMR vaccine raise the risk of ITP?

May 1, 2008

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.

Commentary:

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/.