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Adverse Events Associated with Childhood Vaccines: Evidence Bearing on Causality
the same strains that are used in the United States) were sold and approximately 590,000 children were immunized. One other child had hemolytic-uremic syndrome (as noted above), but the child's platelet count was not reported. Fourteen cases of thrombocytopenia occurred in 18-month-old children. Eight of 13 patients with thrombocytopenia considered to have been vaccine related recovered without therapy. One patient had a second episode, and two patients responded to prednisone therapy within 2 months. Only one patient remained thrombocytopenic at 2 years of follow-up, but that patient had no clinical symptoms. Three other patients had a transient petechial rash, but platelet counts were not determined at the time of the rash.
In 1987, a new passive surveillance system for adverse reactions to vaccines was implemented in Canada (Koch et al., 1989). Five cases of thrombocytopenia were reported to this new system, for a cumulative incidence of 1 case per 100,000 doses of MMR distributed.
Fescharek and colleagues (1990) reported 11 cases of thrombocytopenia following administration of measles vaccine between 1976 and December 1989, over which period an estimated 5.5 million doses of measles and measles-mumps vaccines and MMR were sold in the former West Germany. All cases of thrombocytopenia occurred following immunization with vaccines containing the measles virus antigen (the same strain that is used in the United States). The lowest platelet count was 9,000. All 11 patients recovered either spontaneously or after steroid therapy.
Data suggesting that MMR can cause thrombocytopenic purpura have recently been reported by Nieminen and colleagues (1993). They found that 23 of about 700,000 children immunized with MMR in Finland (which uses the same vaccine strains as those used in the United States) developed thrombocytopenic purpura a mean of 19 days (median, 17 days; range, 7 to 59 days) following vaccination. The patients' ages ranged from 1.2 to 7.3 years. The median platelet nadir was 4,000/mm3, with a range of 1,000 to 45,000/mm3. Fifteen of the patients' platelet counts returned to greater than 100,000 within 1 month, 20 within 2 months, and 22 within 6 months. Thirty months later, one patient had a second episode associated with an infection.
Bone marrow aspirates were performed in 13 patients, and all revealed "at least normal" (p. 268) numbers of megakaryocytes. Platelet survival was decreased in both of the two patients studied, and platelet-associated immunoglobulin was detected in 10 of 15 patients tested. Five of six lost antibodies on follow-up 62 to 206 days after immunization, but one remained weakly positive at 132 days. Five of 15 patients had glycoproteinspecific platelet antibody.
There have been 12 reports in VAERS (submitted between November 1990 and July 1992) of thrombocytopenia following administration of measles