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E bola virus (EBOV) antibodies have been found in populations that have never experienced documented Ebola outbreaks and in persons who reported no history of Ebola virus disease (EVD) (1). The clinical signifi cance of these fi ndings is unknown. We conducted a cross-sectional study in healthy adults and children from a population affected by the 2014-2016 EVD outbreak in Sierra Leone and explored the association of antibody seropositivity and concentration with potential risk factors for EBOV infection. The StudyWe conducted a seroprevalence study in Kambia District, Sierra Leone, during March 2016-June 2018. We nested the study within the screening visit of the EBO-VAC-Salone (https://www.ebovac.org) randomized controlled trial (RCT), which evaluated the safety and immunogenicity of the 2-dose Ad26.ZEBOV, MVA-BN-Filo Ebola vaccine regimen (ClinicalTrials.gov, no. NCT02509494) (2,3). Persons who reported having a previous EVD diagnosis and persons who previously received a candidate Ebola vaccine were ineligible for the RCT, and we excluded them from the seroprevalence study. We recruited adults fi rst, then recruited children in 3 age cohorts: 12-17, 4-11, and 1-3 years of age.We measured IgG to EBOV glycoprotein (GP) by using the Filovirus Animal Non-Clinical Group (FANG) ELISA (Q2 Solutions Vaccine Testing Laboratory, https://www.q2labsolutions.com). We determined seropositivity by using a cutoff of >607 ELISA units (EU)/ mL, which was calculated previously in an EBOV-naive population in West Africa (4) (Appendix, https://wwwnc.cdc.gov/EID/article/28/3/21-1496-App1.pdf).Among 1,282 study participants (Figure), 687 (53.6%) were <18 years of age (median 16 years, IQR 7-25 years), and 827 (64.5%) were male. Among 1,272 participants with antibody results, we considered 107 (8.4%, 95% CI 7.0%-10.0%) seropositive for EBOV GP IgG by using the prespecifi ed cutoff.Risk factor analysis showed that, after adjusting for age and sex, the only characteristic associated with seropositivity was living in a household compound with >1 pigs during the outbreak

We assessed whether the immunogenicity of the two-dose Ad26.ZEBOV, MVA-BN-Filo Ebola vaccine regimen with a 56-day interval between doses was affected by exposure to malaria before dose 1 vaccination and by clinical episodes of malaria in the period immediately after dose 1 and after dose 2 vaccinations. Previous malaria exposure in participants in an Ebola vaccine trial in Sierra Leone (ClinicalTrials.gov: NCT02509494) was classified as low, intermediate, and high according to their antibody responses to a panel of Plasmodium falciparum antigens detected using a Luminex MAGPIX platform. Clinical malaria episodes after vaccinations were recorded as part of the trial safety monitoring. Binding antibody responses against the Ebola virus (EBOV) glycoprotein (GP) were measured 57 days post dose 1 and 21 days post dose 2 by ELISA and summarized as Geometric Mean Concentrations (GMCs). Geometric Mean Ratios (GMRs) were used to compare groups with different levels of exposure to malaria. Overall, 587 participants, comprising 188 (32%) adults (aged ≥ 18 years) and 399 (68%) children (aged 1–3, 4–11, and 12–17 years), were included in the analysis. There was no evidence that the anti-EBOV-GP antibody GMCs post dose 1 and post dose 2 differed between categories of previous malaria exposure. There was weak evidence that the GMC at 57 days post dose 1 was lower in participants who had had at least one episode of clinical malaria post dose 1 compared to participants with no diagnosed clinical malaria in the same period (GMR = 0.82, 95% CI: 0.69–0.98, p-value = 0.02). However, GMC post dose 2 was not reduced in participants who experienced clinical malaria post-dose 1 and/or post-dose 2 vaccinations. In conclusion, the Ad26.ZEBOV, MVA-BN-Filo Ebola vaccine regimen is immunogenic in individuals with previous exposure to malaria and in those who experience clinical malaria after vaccination. This vaccine regimen is suitable for prophylaxis against Ebola virus disease in malaria-endemic regions.