Background: There are differences between Japan and the United States regarding recommended timing of live virus vaccinations after treatment of Kawasaki disease patients with intravenous immune globulin (IVIG): 6 months in Japan and 11 months in the U.S. The prevalence of antibodies to these vaccines using either vaccination schedule remains undetermined. Objective: The present study aimed to evaluate the effectiveness of the live virus vaccination schedule for Kawasaki disease recommended in Japan. Methods: This was a prospective observational study. Kawasaki disease patients aged 6 months and older without past history of or vaccination against measles, rubella, varicella-zoster (VZ), or mumps were enrolled. The children were vaccinated against measles, rubella, VZ, and mumps 6 months after IVIG. Serologic tests for IgG-class specific antibodies to each vaccine virus were performed prior to IVIG; 2 days, 3 months, and 6 months after IVIG, and 3 months after vaccination. The primary outcome was seroprevalence of positive antibodies, which was defined as serum concentration more than 4 IU/mL. Results: A total of 24 children (mean month age 16.8 ± 2.7 at vaccinations, 70.8% male) were enrolled. The rate of measles, rubella, VZ, and mumps seropositivity was 12.5% (3/24), 0% (0/24), 12.5% (3/24), and 0% (0/24), respectively, just before vaccination. The rate increased to 91.7% (22/24), 87.5% (21/24), 20.8% (5/24), and 8.3% (2/24), respectively, 3 months after vaccination. There were no serious adverse events. Conclusions: Use of the Japanese vaccination schedule led to extremely low seroprevalence of VZ and mumps antibodies but acceptable seroprevalence of measles and rubella antibodies. This study is ongoing and more cases (up to 30, the target sample size) are needed before the appropriateness of the timing of vaccination in Japan can be discussed.
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