Christian M. Kahusu a,b,c,*, Laur`ene Peckeu-Abboud h, Odin Goovaerts b, ´Elys´ee Matungulu a, Leo Heyndrickx d, Kevin K. Ari¨en d, Selien Oostvogels b, Ange Mubiala a, Saidou Milua a, Ilombe Myriam Mbilizi a, Samuel Shamamba a, Naomie Bayoka a, Elie Ishara-Nshombo g, C´elestin Tshimanga a, Antoine Nkuba i,k, Martine Peeters f, Bobo Bazola a, Jessy Sabue a, Michel Ngimba g, No¨ella Mukanya g, Patrick Tshita a, Christian Kinzungu a, Dacquin M. Kasumba a,k, Olivier Tshiani l, Placide Mbala-Kingebeni j,k, Laurens Liesenborghs c,e, Daniel Mukadi-Bamuleka g,i,k, Sabue Mulangu a,k,m, Hugo Kavunga-Membo g,i,k,1, Wim Adriaensen b,1

a Clinical Immunology Department, Institut national de recherche biom´edicale (INRB), Kinshasa, Congo
b Clinical Immunology Unit, Department of Clinical Sciences, Institute of Tropical Medicine (ITM), Antwerp, Belgium
c Virology, Antiviral Drug & Vaccine Research Group, Department of Microbiology, Immunology and Transplantation, KU Leuven (KUL), Belgium
d Virology Unit, Department of Biomedical Sciences, Institute of Tropical Medicine (ITM), Antwerp, Belgium
e Clinical Emerging Infectious Diseases, Department of Clinical Sciences, Institute of Tropical Medicine (ITM), Antwerp, Belgium
f Institut de recherche pour le d´eveloppement IRD Montpellier, Montpellier, France
g Rodolphe M´erieux Institut National de Recherche Biom´edicale Goma, Goma, North Kivu, Congo
h Haute Autorit´e de Sant´e (HAS), French NITAG, Paris, France
i Virology Departement, Institut national de recherche biom´edicale (INRB), Kinshasa, Congo
j Epidemiology and Global Health Department, Institut national de recherche biom´edicale (INRB), Kinshasa, Congo
k Service of Microbiology, Department of Medical Biology, Faculty of Medicine, University of Kinshasa, Congo
l Clinical Monitoring Research Program Directorate, Frederick National Laboratory for Cancer Research, Frederick, MD, USA
m Ridgeback Biotherapeutics, Miami, FL, USA

A B S T R A C T

Zaïre ebolavirus (EBOV) remains a serious threat with a high case fatality rate in humans, particularly in the Democratic Republic of Congo (DRC). To cope with previous epidemics, the single-dose and prophylactic rVSVZEBOV vaccine was widely applied. However, evidence on the duration of protection and, consequently, the
need or timing for booster doses is lacking. Therefore, we investigated in a cross-sectional study design the antibody persistence and neutralizing capacity against three strains of the Orthoebolavirus zaïrense species
within healthcare workers (HCWs) who were previously vaccinated in different outbreaks across DRC. The
presence of vector-directed immunity was studied via seropositivity to VSV proteins.
In total, 133 HCWs were recruited and grouped according to their time from initial vaccination (1􀀀 2, 2􀀀 3, >3
years), in addition to a control group of 20 unvaccinated HCWs. In 1–2 year vaccinated participants (n = 10), an
overall high antibody response (100 % seropositivity) specific to the vaccine-targeted EBOV glycoprotein (GP) of
the Kikwit strain was observed, in comparison to <50 % seropositivity to the Mayinga and Kissidougou GP EBOV
variants. This antibody trend persisted up to 4 years after vaccination, but overall seropositivity rates decreased
to 76.8 % (Kikwit), 38.3 % (Mayinga), and 44.6 % (Kissidougou) for participants vaccinated >3 years ago. Only a
minority (n = 6) among all time groups of HCWs with high antibody titers still had demonstrable neutralizing
capacity. No persistent VSV-specific antibody responses were observed at any time, suggesting no to low
interference with booster doses.

https://doi.org/10.1016/j.vaccine.2025.127537
Received 3 March 2025; Received in revised form 17 July 2025; Accepted 18 July 2025
Vaccine 62 (2025) 127537
0264-410X/© 2025 Published by Elsevier Ltd.