Investigators from three United Kingdom institutions in Sutton, London, and Manchester evaluated the vaccine-specific antibody persistence and immunogenicity of five childhood vaccines (MMR, tetanus toxoid, IPV, Hib conjugate, and meningococcus C [MCC]) after completion of chemotherapy for acute lymphocytic leukemia (ALL) and acute myeloid leukemia (AML). Fifty-nine previously vaccinated children ages 1–18 years who had completed treatment for ALL or AML at least six months earlier were enrolled over a two-year period. Patients were revaccinated with one dose each of DTaP, IPV, Hib, Measles (administered as MMR), and MCC. Blood samples for serologic testing were obtained on the day of vaccination, at two to four weeks, and one year later. For each of the five vaccines, there was a significant rise in the antibody level after revaccination. There was no statistical association for any of the five vaccines between the increase in antibody level and length of time between vaccination and the completion of treatment, patient age at diagnosis, revaccination age, past vaccination history, or treatment regimen. Patients with ALL had a significantly higher antibody level to Hib, tetanus toxoid, and IPV compared to patients with AML.
Prior to the diagnosis of leukemia, 95% of the patients had received at least 1 dose of Hib; 86.5% had protective antibody levels prior to revaccination. Overall, 75% had a fourfold or greater increase in antibody post-vaccination, and 100% achieved a level ≥0.15 μg/ml (indicative of short-term protection) and 93% reached ≥1.0 μg/ml (indicative of long-term protection). Although the antibody level decreased after one year, it remained ≥1.0 μg/ml in all patients.
For tetanus toxoid and IPV, all patients had received three doses before diagnosis of leukemia. For tetanus toxoid, 90% had a four-fold or greater increase in antibody concentration after revaccination with all achieving a level sufficient for long-term protection. For IPV, 11% had protective antibody levels to all three polioviruses before revaccination. After revaccination 85% achieved protective levels for all three serotypes. At 12 months there was a decrease in antibody level, with only 47% of patients having protective levels of antibodies for all three serotypes.
For measles, 92% of the patients had received at least one dose of MMR prior to the diagnosis of leukemia. Before vaccination, 73.5% of the patients had antibody levels thought to be protective, increasing to 94% of patients after revaccination. Levels decreased after 12 months, but were still protective.
Prior to the diagnosis of leukemia only 40% of patients had received MCC vaccine. Among these patients 17% had protective titers before chemotherapy, increasing to 98% after revaccination. There was insufficient serum available to assess titers 12 months after vaccination.
The authors conclude that re-immunization with one dose of most vaccines six months following completion of chemotherapy for ALL or AML provides protection against disease in most children.
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