The Sudan virus (SUDV) outbreaks in recent years, including the most recent outbreak in Uganda, created a public health emergency in the eastern Africa region. There are no licensed vaccines or therapeutics approved against SUDV; however, we have previously developed a vesicular stomatitis virus (VSV)-based vaccine expressing the SUDV glycoprotein and showed its single-dose efficacy in non-human primates (NHPs) with pre-existing Ebola virus (EBOV) immunity. Here, we determined the fast-acting capacity of this vaccine in naive NHPs. In addition, we examined if the licensed VSV-EBOV vaccine would provide any prophylactic benefit against SUDV infection. We used four groups of male cynomolgus macaques (n=6 per group) aged 2·5-4·5 years and weighing 2·9-5·2 kg. NHPs were vaccinated by intramuscular injection 28 days before challenge with either 1 × 10⁷ plaque-forming units (PFUs) VSV-SUDV, VSV-EBOV, or control vaccine (VSV-LASV). Another group was vaccinated with 1 × 10⁷ PFU VSV-SUDV 7 days before challenge. On day 0, all 24 NHPs were challenged with a lethal dose of SUDV (1 × 10⁴ 50% tissue culture infectious doses [TCID₅₀] SUDV-Gulu, backtitred as 1·1 × 10⁴ TCID₅₀). We assessed anaesthetised NHPs on days -28, -21, -14, and -7 before challenge; days 0, 3, 6, 9, 14, 21, 28, and 35 after challenge; and at euthanasia (day 42 for survivors). All VSV-SUDV-vaccinated NHPs were protected from disease after the lethal SUDV challenge. In contrast, the VSV-EBOV-vaccinated and control NHPs succumbed to disease between days 5 and 7 after challenge presenting with classical signs of Sudan virus disease associated with high-titre viraemia (>1 × 10⁸ TCID₅₀ per mL), high viral organ load (>1 × 10⁸ TCID₅₀ per g), dysregulated cytokine profiles, and typical pathological changes. The humoral immune response in the NHPs vaccinated with VSV-SUDV 1 month before challenge resulted in a profound and sustained serum antibody response (20 000-30 000 U/mL) with a diverse functionality profile (antibody-dependent cellular phagocytosis and antibody-dependent complement), which was not observed to the same extent in NHPs vaccinated 1 week before challenge. We showed that a single dose of VSV-SUDV protected NHPs from lethal SUDV infection within 1 week. The fast-acting nature highlights VSV-SUDV as an ideal countermeasure for ring vaccination during outbreaks of Sudan virus disease pending further preclinical and clinical assessment. In contrast, VSV-EBOV provided no relevant protection against SUDV infection in NHPs, highlighting the need for species-specific filovirus vaccines. National Institutes of Health, US Department of Health and Human Services.

Marburg virus (MARV), a filovirus, was first identified in 1967 in Marburg, Germany, and Belgrade, former Yugoslavia. Since then, MARV has caused sporadic outbreaks of human disease with high case fatality rates in parts of Africa, with the largest outbreak occurring in 2004/05 in Angola. From 2021 to 2023, MARV outbreaks occurred in Guinea, Ghana, New Guinea, and Tanzania, emphasizing the expansion of its endemic area into new geographical regions. There are currently no approved vaccines or therapeutics targeting MARV, but several vaccine candidates have shown promise in preclinical studies. We compared three vaccine platforms simultaneously by vaccinating hamsters with either a single dose of an adenovirus-based (ChAdOx-1 MARV) vaccine, an alphavirus replicon-based RNA (LION-MARV) vaccine, or a recombinant vesicular stomatitis virus-based (VSV-MARV) vaccine, all expressing the MARV glycoprotein as the antigen. Lethal challenge with hamster-adapted MARV 4 weeks after vaccination resulted in uniform protection of the VSV-MARV and LION-MARV groups and 83% of the ChAdOx-1 MARV group. Assessment of the antigen-specific humoral response and its functionality revealed vaccine-platform-dependent differences, particularly in the Fc effector functions.

Ebola virus disease (EVD) remains among the biggest public health threats in Africa, even though recently a vaccine was approved for human use. However, in outbreak situations treatment strategies are needed in combination with vaccination campaigns to impact and stop the spread of the disease. Here, we discuss the development of the immunotherapeutics against EDV both targeting the virus itself and bolstering the immunological environment of the host at both the pre-clinical and clinical level. The early development of antibody therapy in preclinical settings and the early pitfalls in the implementation of this therapeutic strategy are discussed. We also consider the advancement of the production, modulation, and specificity of the antibody treatment that garnered increased success in preclinical studies to the point that it was warranted to test them in a clinical setting. Initial clinical trials in an outbreak scenario proved difficult to definitively confirm the efficacy of the implemented treatment. Upon further modification and with the experiences from the challenging outbreak conditions in mind, the PALM clinical trial demonstrated efficacy of an antibody cocktail which recently received approval for human use.

Lack of Lloviu Virus Disease in Ferret Model

The filovirus, Ebola virus (EBOV), causes outbreaks of EBOV disease (EVD) throughout equatorial Africa. ERVEBO is a replication-competent recombinant vesicular stomatitis virus-vectored vaccine encoding the EBOV glycoprotein (recombinant vesicular stomatitis virus [rVSV]/EBOV), which is licensed to control EVD outbreaks. EVD outbreaks occur in regions endemic for Plasmodium -caused malaria. Plasmodium infections persist due in part to the parasite’s ability to evade sterilizing immunity, which also dampens immune responses to heterologous vaccines. Acute murine Plasmodium infection at the time of rVSV/EBOV vaccination reduced vaccine-mediated protection against mouse-adapted EBOV (ma-EBOV) challenge. Decreased protection was associated with a Plasmodium- induced interferon gamma-mediated decrease of rVSV/EBOV replication in lymph node macrophages, resulting in reduced primary anti-EBOV glycoprotein antibody responses. Higher doses of rVSV/EBOV partially overcame the antibody deficits and elicited protective responses. Evidence of the negative impact of Plasmodium on the efficacy of low-dose rVSV/EBOV vaccine protocols supports the use of high antigen loads in the effective management of EVD outbreaks. IMPORTANCE: We show that a blood-stage murine Plasmodium infection negatively impacts the primary antibody response elicited by low-dose recombinant vesicular stomatitis virus (rVSV)/Ebola virus (EBOV) vaccination and results in reduced protection against a lethal dose of mouse-adapted EBOV. This defect occurs within the draining lymph node due to the elevation of interferon gamma elicited in Plasmodium yoelii ( Py) -infected mice. The Py -imposed decrease in vaccine-mediated protection can be overcome with higher doses of rVSV/EBOV. While the strong protection conferred by rVSV/EBOV and significant side effects known to be associated with this vaccine have led to the suggestion that the vaccine dosage be reduced, our studies provide a rationale for maintaining the current higher dose.