Baseline Asymptomatic Malaria Infection and Immunogenicity of rVSVΔG-ZEBOV-GP Vaccine: The Sierra Leone Trial to Introduce a Vaccine Against Ebola (STRIVE).

BACKGROUND The effect of malaria infection on rVSVΔG-ZEBOV-GP (ERVEBO®) immunogenicity is unknown. METHODS The Sierra Leone Trial to Introduce a Vaccine against Ebola (STRIVE) vaccinated 7998 asymptomatic adults with rVSVΔG-ZEBOV-GP during the 2014-6 Ebola epidemic. In STRIVE's immunogenicity sub-study, participants provided blood samples at baseline, 1, 6, and 9-12 months. Anti-glycoprotein (GP) binding and neutralizing antibodies were measured using validated assays. Baseline samples were tested for malaria parasites by PCR. RESULTS Overall, 506 participants enrolled in the immunogenicity sub-study and had ≥1 post-vaccination antibody titer. Of 499 participants with a result, baseline malaria parasitemia was detected in 73(14.6%). All GP-ELISA and plaque reduction neutralization test (PRNT) geometric mean titers (GMTs) at 1, 6, and 9-12 months were above baseline, and 94.1% of participants seroresponded by GP-ELISA (≥2-fold rise AND ≥200 EU/ml), while 81.5% seroresponded by PRNT (≥4-fold rise) at ≥1 post-vaccination assessment. In participants with baseline malaria parasitemia, the PRNT seroresponse proportion was lower, while PRNT GMTs and GP-ELISA seroresponse and GMTs showed a trend toward lower responses at 6 and 9-12 months. CONCLUSION Asymptomatic adults with and without malaria parasitemia had robust immune responses to rVSVΔG-ZEBOV-GP persisting for 9-12 months. Responses in those with malaria parasitemia were somewhat lower.