Researchers are evaluating the effectiveness of an Ebola vaccine against the current Bundibugyo species of orthoebolaviruses in the Democratic Republic of Congo (DRC). The report states that no vaccine has been developed against the Bundibugyo virus (BDBV), and the outbreak is expected to exceed the 2013-2016 epidemic.
Megan Halbrook, PhD, and colleagues from the University of California, Los Angeles, investigated whether currently licensed Ebola virus disease vaccines could generate cross-reactive immune responses relevant to the current outbreak. They identified 482 individuals in Mbandaka and 505 in Beni who had received the rVSV∆-ZEBOV-GP vaccine in 2018.
Evaluation of Cross-Reactive Antibody Response
The investigators assessed the longitudinal cross-reactive antibody response to the EBOV and non-EBOV species after receiving the rVSV∆-ZEBOV-GP vaccine. They used a pan-filovirus multiplex immunoassay, with seroreactivity expressed in units of median fluorescent intensity (MFI). Both regions had experienced recurrent outbreaks with multiple Orthoebolavirus species during the study period.
The researchers found that at baseline, 16 (3%) of the Mbandaka cohort and 62 (10%) in Beni had been seroreactive to BDBV glycoprotein. In Mbandaka, BDBV glycoprotein antibody reactivity remained stable at 6 months after vaccination, before increasing from a mean MFI of 1238 at 2.5 years to 4845 at 3.5 years. In Beni, BDBV reactivity increased rapidly after vaccination to a mean MFI of 6678 with 283 (52%) seroreactive at 21 days.
Factors Influencing Seroreactivity
Halbrook and colleagues noted that the differing patterns of BDBV glycoprotein seroreactivity observed between Beni and Mbandaka warrant further investigation into the epidemiological and immunological factors associated with this seroreactivity. They suggest that factors not related to vaccination, such as previous filovirus exposure, immune priming, and environmental conditions, could have influenced BDBV glycoprotein seroreactivity.
Abhishek Prasad, PhD, and Thomas Geisbert, PhD, from the University of Texas Medical Branch, commented that this study, like the earlier PREVAC trial, is limited in that it only measured the presence and relative magnitude of BDBV-reactive antibodies. They warned that vaccination can induce complacency in health-care workers and community members, leading to the relaxation of infection avoidance measures and increased transmission if the vaccine is not fully protective.
According to the report, the study’s results will be published in The Lancet.
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