Although the MMR vaccine has been linked to a heightened risk of a rare blood disorder, other childhood vaccines do not appear to be, researchers reported on January 09. The disorder is called immune thrombocytopenic purpura, or ITP, and it arises when the immune system destroys blood cells called platelets.
That limits the blood's ability to clot, which can cause bleeding under the skin, bruising and nosebleeds - or, in rare cases, serious problems like bleeding in the brain. Doctors have long known that the MMR vaccine against measles, mumps and rubella can cause ITP - usually triggering a mild, temporary case. It's estimated that ITP arises once for every 40,000 MMR shots. But it had not been clear whether any other childhood vaccines might cause ITP.
"It's such a rare disease to start with, and then it would only rarely be triggered by a vaccine," said Dr. Sean T. O'Leary of Children's Hospital Colorado in Aurora, the lead researcher on the new study.
So for their study, O'Leary and his colleagues looked at medical records for 1.8 million US infants and children who received routine vaccines between 2000 and 2009. Over that time, 197 kids were diagnosed with ITP. The researchers compared a child's risk of developing ITP within 42 days of receiving a vaccine compared with other times. And they found no evidence that any vaccine other than MMR was linked to an increased risk of ITP in young children. The picture was different, however, with older kids, the researchers report in the journal Pediatrics.
Among 7- to 17-year-olds, hepatitis A vaccination was tied to an increased ITP risk. And in 11- to 17-year-olds, the chickenpox vaccine and the vaccine against tetanus, diphtheria and acellular pertussis (Tdap) were both linked to the blood disorder. However, that was based on just one or two cases of ITP tied to each vaccine.
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