2279. A Randomized Open-Label Trial of 2-Dose or 3-Dose Primary Rabies Immunization Among Thai Children

BACKGROUND: The World Health Organization (WHO) recently recommended 2-dose primary rabies immunization instead of the 3-dose standard regimen. Given limited data of 2-dose regimens in pediatric population, this study was conducted. The objective was to compare the immunogenicity between 2-dose and 3-dose primary rabies immunization. METHODS: This study was an open-label clinical trial. Inclusion criteria were children aged 2–12 years with rabies virus neutralizing antibody (RVNA) titers < 0.5 IU/ml at baseline. The participants were divided into 2-dose vaccination (2D) on days 0 and 28 and 3-dose vaccination (3D) on days 0, 7, and 28 with a 2:1 ratio. A dose of 0.5 ml purified vero cell rabies vaccine (PVRV) was administered intramuscularly. RVNA titers were measured at 14-day post primary immunization. RVNA titers ≥ 0.5 IU/ml were considered seroprotective against rabies. Geometric mean titers (GMT) were calculated. T cell specific response to rabies vaccine antigen were measured from peripheral blood mononuclear cells (PBMCs) using the interferon-gamma enzyme-linked immunospot (IFN-gamma ELISpot) assay. RESULTS: From September to October 2017, 105 participants (52% male), 76 in 2D group and 29 in 3D group were enrolled. Median age and body weight was 70 months (IQR 53–88) and 19.2 kilograms (IQR 15.9–24.3), respectively. All participants had seroprotection at 14-day post primary immunization with GMT of 18.6 (95% CI 15.8-21.9) and 16.3 (95% CI 13.1–20.0) in 2D and 3D groups, respectively (P = 0.35). Median IFN-gamma level at 14-day post primary immunization was 60 spot forming cells (SFC) per 10(6)PBMCs and 132 SFC per 10(6)PBMCs in the 2D and 3D groups, respectively (P = 0.15). CONCLUSION: The immunogenicity of 2-dose primary rabies immunization at 14-day post primary vaccination is comparable to the 3-dose regimen. Participants are currently being followed for 1-year results. DISCLOSURES: All authors: No reported disclosures.