Therapeutic vaccination strategies against EBOV by rVSV-EBOV-GP: the role of innate immunity

Improving Ebola virus disease outbreak control through targeted post-exposure prophylaxis

Ebola virus disease kills more than half of people infected. Since the disease is transmitted via close human contact, identifying individuals at the highest risk of developing the disease is possible on the basis of the type of contact (correlated with viral exposure). Different candidates for post-exposure prophylaxis (PEP; ie, vaccines, antivirals, and monoclonal antibodies) each have their specific benefits and limitations, which we discuss in this Viewpoint. Approved monoclonal antibodies have been found to reduce mortality in people with Ebola virus disease. As monoclonal antibodies act swiftly by directly targeting the virus, they are promising candidates for targeted PEP in contacts at high risk of developing disease. This intervention could save lives, halt viral transmission, and, ultimately, help curtail outbreak propagation. We explore how a strategic integration of monoclonal antibodies and vaccines as PEP could provide both immediate and long-term protection against Ebola virus disease, highlighting ongoing clinical research that aims to refine this approach, and discuss the transformative potential of a successful PEP strategy to help control viral haemorrhagic fever outbreaks.

Case fatality risk among individuals vaccinated with rVSVΔG-ZEBOV-GP: a retrospective cohort analysis of patients with confirmed Ebola virus disease in the Democratic Republic of the Congo

BACKGROUND

The rVSVΔG-ZEBOV-GP vaccine constitutes a valuable tool to control Ebola virus disease outbreaks. This retrospective cohort study aimed to assess the protective effect of the vaccine against death among patients with confirmed Ebola virus disease.

METHODS

In this retrospective cohort analysis of patients with confirmed Ebola virus disease admitted to Ebola health facilities in the Democratic Republic of the Congo between July 27, 2018, and April 27, 2020, we performed univariate and multivariate analyses to assess case fatality risk and cycle threshold for nucleoprotein according to vaccination status, Ebola virus disease-specific treatments (eg, mAb114 and REGN-EB3), and other risk factors.

FINDINGS

We analysed all 2279 patients with confirmed Ebola virus disease. Of these 2279 patients, 1300 (57%) were female and 979 (43%) were male. Vaccination significantly lowered case fatality risk (vaccinated: 25% [106/423] vs not vaccinated: 56% [570/1015]; p<0·0001). In adjusted analyses, vaccination significantly lowered the risk of death compared with no vaccination, with protection increasing as time elapsed from vaccination to symptom onset (vaccinated ≤2 days before onset: 27% [27/99], adjusted relative risk 0·56 [95% CI 0·36-0·82, p=0·0046]; 3-9 days before onset: 20% [28/139], 0·44 [0·29-0·65, p=0·0001]; ≥10 days before onset: 18% [12/68], 0·40 [0·21-0·69; p=0·0022]; vaccination date unknown: 33% [39/117], 0·69 [0·48-0·96; p=0·0341]; and vaccination status unknown: 52% [441/841], 0·80 [0·70-0·91, p=0·0011]). Longer time from symptom onset to admission significantly increased risk of death (49% [1117/2279], 1·03 [1·02-1·05; p<0·0001]). Cycle threshold values for nucleoprotein were significantly higher-indicating lower viraemia-among patients who were vaccinated compared with those who were not vaccinated; the highest difference was observed among those vaccinated 21 days or longer before symptom onset (median 30·0 cycles [IQR 24·6-33·7]) compared with patients who were not vaccinated (21·4 cycles [18·4-25·9], p<0·0001).

INTERPRETATION

To our knowledge, this is the first observational study describing the protective effect of rVSVΔG-ZEBOV-GP vaccination against death among patients with confirmed Ebola virus disease admitted to an Ebola health facility. Vaccination was protective against death for all patients, even when adjusted for Ebola virus disease-specific treatment, age group, and time from symptom onset to admission.

FUNDING

Médecins Sans Frontières.

TRANSLATION

For the French translation of the abstract see Supplementary Materials section.

Oral Immunization with rVSV Bivalent Vaccine Elicits Protective Immune Responses, Including ADCC, against Both SARS-CoV-2 and Influenza A Viruses

COVID-19 and influenza both cause enormous disease burdens, and vaccines are the primary measures for their control. Since these viral diseases are transmitted through the mucosal surface of the respiratory tract, developing an effective and convenient mucosal vaccine should be a high priority. We previously reported a recombinant vesicular stomatitis virus (rVSV)-based bivalent vaccine (v-EM2/SPΔC1Delta) that protects animals from both SARS-CoV-2 and influenza viruses via intramuscular and intranasal immunization. Here, we further investigated the immune response induced by oral immunization with this vaccine and its protective efficacy in mice. The results demonstrated that the oral delivery, like the intranasal route, elicited strong and protective systemic immune responses against SARS-CoV-2 and influenza A virus. This included high levels of neutralizing antibodies (NAbs) against SARS-CoV-2, as well as strong anti-SARS-CoV-2 spike protein (SP) antibody-dependent cellular cytotoxicity (ADCC) and anti-influenza M2 ADCC responses in mice sera. Furthermore, it provided efficient protection against challenge with influenza H1N1 virus in a mouse model, with a 100% survival rate and a significantly low lung viral load of influenza virus. All these findings provide substantial evidence for the effectiveness of oral immunization with the rVSV bivalent vaccine.

Rapid protection of nonhuman primates against Marburg virus disease using a single low-dose VSV-based vaccine

BACKGROUND

Marburg virus (MARV) is the causative agent of Marburg virus disease (MVD) which has a case fatality rate up to ∼90% in humans. Recently, there were cases reported in Guinea and Ghana highlighting this virus as a high-consequence pathogen potentially threatening global public health. There are no licensed treatments or vaccines available today. We used a vesicular stomatitis virus (VSV)-based vaccine expressing the MARV-Angola glycoprotein (VSV-MARV) as the viral antigen. Previously, a single dose of 1 × 10⁷ plaque-forming units (PFU) administered 7 days before challenge resulted in uniform protection from disease in cynomolgus macaques.

METHODS

As we sought to lower the vaccination dose to achieve a higher number of vaccine doses per vial, we administered 1 × 10⁵ or 1 × 10³ PFU 14 days or 1 × 10³ PFU 7 days before challenge to cohorts of cynomolgus macaques and investigated immunity as well as protective efficacy.

RESULTS

Vaccination resulted in uniform protection with no detectable viremia. Antigen-specific IgG responses were induced by both vaccine concentrations and were sustained until the study endpoint. Neutralizing antibody responses and antibody-dependent cellular phagocytosis were observed. The cellular response after vaccination was characterized by an early induction of NK cell activation. Additionally, antigen-specific memory T cell subsets were detected in all vaccination cohorts indicating that while the primary protective mechanism of VSV-MARV is the humoral response, a functional cellular response is also induced.

INTERPRETATION

Overall, this data highlights VSV-MARV as a viable and fast-acting MARV vaccine candidate suitable for deployment in emergency outbreak situations and supports its clinical development.

FUNDING

This work was funded by the Intramural Research Program NIAID, NIH.