Immunogenicity of a live-attenuated Japanese encephalitis vaccine in children and adolescents after hematopoietic stem cell transplantation

There have been no recommendations for revaccination with the Japanese encephalitis (JE) vaccine in post-hematopoietic stem cell transplantation (HSCT) patients. This study aimed to measure the immunogenic response to a live-attenuated JE vaccine (SA 14-14-2) in post-HSCT patients. JE-specific neutralizing Ab titers were measured before and after the JE vaccination. The patients with Ab titers <10 at the 3-month time point received a second injection at 6 months. A total of 28 patients (male:female = 11:17) with a median age of 13 years (4-21 years) were included. The underlying diseases were thalassemia (50%) and hematologic malignancies (50%). Ten patients (35.7%) had Ab titers above the preventive level before vaccination. Nine of 18 patients (50%) seroconverted at 3 months after a single JE vaccination, but only three of these patients had sustained protective Ab levels. Seven of nine patients (78%) seroconverted at 3 months after a second JE vaccine injection, and all of these patients sustained protective Ab levels at 12 months. In conclusion, post-HSCT patients had low seroconversion rates after a single dose of the live-attenuated JE vaccine. These patients may require at least two doses of the JE vaccine to ensure protective Ab levels.