Safety of early immunization against measles/mumps/rubella after bone marrow transplantation

Machado et al recently reported on their experience of an outbreak of measles in Brazil and its impact on their bone marrow transplantation (BMT) population.1 They comment that one of the major reasons these patients were not immunized is that fewer than 2 years had passed since receiving BMT, and no data are available concerning the safety and effectiveness of measles immunization before the second year after BMT. This is despite a national study of immunization practices following allogeneic BMT in the United States, which indicated that the measles, mumps, and rubella (MMR) immunization was being administered at 12 months or earlier after BMT in 22% of centers performing transplantions on children younger than 7 years of age, and in 12% of centers performing transplantions on children aged 7 years or older.2 As we dealt with a pediatric population, we were concerned that our BMT recipients were vulnerable to infection with measles during the 2-year interval between BMT and the time recommended for MMR vaccination. This was illustrated when one of our patients developed measles at 9 months after BMT. We therefore initiated a protocol firstly of catch-up immunization in patients who had not been previously immunized, and then of offering immunization against MMR in the second year after BMT.

We reviewed our experience at the BMT follow-up clinic at the Children's Hospital Westmead (CHW) with MMR vaccination after BMT. We have immunized 79 patients with a live attenuated trivalent vaccine directed against MMR (0.5 mL MMR-II, Merck Sharpe and Dohme, Sydney, Australia) since November 1990. MMR was administered at a median time of 13 months after BMT. To be eligible for MMR immunization, patients had to be recipients of either autografts or allografts who were more than 12 months after BMT, without cGvHD, and off all immunosuppressives for at least 3 months. One child vaccinated 24 months after allogeneic BMT developed a transient rash and fever one week after vaccination. He suffered no serious complications. None of the other 78 patients who were vaccinated suffered any adverse consequences.

By the time of immunization, patients had infrequent visits to CHW, and so adequate prevaccination and postvaccination serology results were available on only 44 patients. Immunization against rubella was effective from 12 months after BMT onwards. Of the 34 patients seronegative to rubella prior to immunization, 91% became seropositive after MMR immunization. Of the 35 patients seronegative to measles prior to immunization, 16 (46%) became seropositive after MMR immunization. There was a significantly higher rate of seroconversion to measles in children who were immunized at more than 15 months after BMT (35% prior to versus 78% after 15 months; Fisher exact,P = .05). There was no significant relationship between seroconversion to measles or rubella and any of the following variables: age, sex, diagnosis, prior GVHD, or type of BMT donor.

In our experience, MMR vaccination between 12 and 24 months after BMT is safe. It provides effective immunity against rubella; the 91% rate of seroconversion to rubella is comparable to rates of 75% and 90% previously reported. The overall rate of seroconversion to measles of 46% is unsatisfactory but indicates that MMR vaccination is effective against measles in some children in the second year following BMT. We are routinely recommending MMR reimmunization at 15 months after BMT, and it can be safely given earlier if measles or rubella is in the community. However, serology should be performed following vaccination to confirm effective immunization against measles.