Persistence of immunological memory as a potential correlate of long-term, vaccine-induced protection against Ebola virus disease in humans

Lot-to-lot consistency, immunogenicity, and safety of the Ad26.ZEBOV, MVA-BN-Filo Ebola virus vaccine regimen: A phase 3, randomized, double-blind, placebo-controlled trial

This phase-3, double-blind, placebo-controlled study (NCT04228783) evaluated lot-to-lot consistency of the Ad26.ZEBOV, MVA-BN-Filo Ebola vaccine regimen. Participants were randomized (6:6:6:1) to receive the two-dose regimen from three consecutively manufactured lots of Ad26.ZEBOV on Day 1 paired with three consecutively manufactured lots of MVA-BN-Filo on Day 57 (Groups 1-3) or two doses of placebo (Group 4). An additional cohort also received an Ad26.ZEBOV booster or placebo 4 months post-dose 2. Equivalence of the immunogenicity at 21 days post-dose 2 between any two groups was demonstrated if the 95% confidence interval (CI) of the Ebola virus glycoprotein (EBOV GP)-binding antibody geometric mean concentration (GMC) ratio was entirely within the prespecified margin of 0.5-2.0. Lot-to-lot consistency (i.e., consecutive lots can be consistently manufactured) was accomplished if equivalence was shown for all three pairwise comparisons. Results showed that the primary objective in the per-protocol immunogenicity subset (n = 549) was established for each pairwise comparison (Group 1 vs 2: GMC ratio = 0.9 [95% CI: 0.8, 1.1], Group 1 vs 3: 0.9 [0.8, 1.1], Group 2 vs 3: 1.0 [0.9, 1.2]). Equivalence of the three groups for the Ad26.ZEBOV component only was also demonstrated at 56 days post-dose 1. EBOV GP-binding antibody responses (post-vaccination concentrations >2.5-fold from baseline) were observed in 419/421 (99.5%) vaccine recipients at 21 days post-dose 2 and 445/460 (96.7%) at 56 days post-dose 1. In the booster cohort (n = 39), GMCs increased 9.0- and 11.8-fold at 7 and 21 days post-booster, respectively, versus pre-booster. Ad26.ZEBOV, MVA-BN-Filo was well tolerated, and no safety issues were identified.

Ad26.ZEBOV, MVA-BN-Filo Ebola virus disease vaccine regimen plus Ad26.ZEBOV booster at 1 year versus 2 years in health-care and front-line workers in the Democratic Republic of the Congo: secondary and exploratory outcomes of an open-label, randomised, phase 2 trial

BACKGROUND

Health-care providers and front-line workers are at risk of contracting Ebola virus disease during an Ebola virus outbreak and consequently of becoming drivers of the disease. We aimed to assess the long-term immunogenicity of the Ad26.ZEBOV, MVA-BN-Filo vaccine regimen and the safety of and immune memory response to an Ad26.ZEBOV booster vaccination at 1 year or 2 years after the first dose in this at-risk population.

METHODS

This open-label, single-centre, randomised, phase 2 trial was conducted at one study site within a hospital in Boende, Democratic Republic of the Congo. Adult health-care providers and front-line workers, excluding those with a known history of Ebola virus disease, were vaccinated with a two-dose heterologous regimen administered at a 56-day interval via a 0·5 mL intramuscular injection in the deltoid muscle, comprising Ad26.ZEBOV as the first dose and MVA-BN-Filo as the second dose. After the initial vaccination on day 1, participants were randomly assigned (1:1) via randomisation envelopes, opened in a sequential order, to receive an Ad26.ZEBOV booster vaccination at 1 year (group 1) or 2 years (group 2) after the first dose. We present the secondary and exploratory objectives of the trial-results of the primary objective have been published elsewhere. We measured immunogenicity at six timepoints per group as geometric mean concentrations (GMCs) of Ebola virus glycoprotein-specific IgG binding antibodies, using the Filovirus Animal Non-Clinical Group ELISA. We assessed serious adverse events occurring up to 6 months after the last dose and local and systemic solicited and unsolicited adverse events reported for 7 days after the booster vaccination. Antibody responses were analysed per protocol, serious adverse events per full analysis set (FAS), and adverse events for all boosted FAS participants. This trial is registered as completed on ClinicalTrials.gov (NCT04186000).

FINDINGS

Between Dec 18, 2019, and Feb 8, 2020, 699 health-care providers and front-line workers were enrolled and 698 were randomly assigned (350 to group 1 and 348 to group 2 [FAS]); 534 (77%) participants were male and 164 (23%) were female. 319 in group 1 and 317 in group 2 received the booster. 29 (8%) in group 1 and 26 (7%) in group 2 did not complete the study, mostly due to loss to follow-up or moving out of the study area. In both groups, injection-site pain or tenderness (87 [27%] of 319 group 1 participants vs 90 [28%] of 317 group 2 participants) and headache (91 [29%] vs 93 [29%]) were the most common solicited adverse events related to the investigational product. One participant (in group 2) had a related serious adverse event after booster vaccination (fever of ≥40·0°C). Before booster vaccination, Ebola virus glycoprotein-specific IgG binding antibody GMCs were 279·9 ELISA units (EU) per mL (95% CI 250·6-312·7) in 314 group 1 participants (1 year after first dose) and 274·6 EU/mL (242·1-311·5) in 310 group 2 participants (2 years after first dose). These values were 5·2 times higher in group 1 and 4·9 times higher in group 2 than before vaccination on day 1. 7 days after booster vaccination, these values increased to 10 781·6 EU/mL (9354·4-12 426·4) for group 1 and 10 746·9 EU/mL (9208·7-12 542·0) for group 2, which were approximately 39 times higher than before booster vaccination in both groups. 1 year after booster vaccination in 299 group 1 participants, a GMC that was 7·6-times higher than before booster vaccination was still observed (2133·1 EU/mL [1827·7-2489·7]).

INTERPRETATION

Overall, the vaccine regimen and booster dose were well tolerated. A similar and robust humoral immune response was observed for participants boosted 1 year and 2 years after the first dose, supporting the use of the regimen and flexibility of booster dose administration for prophylactic vaccination in at-risk populations.

FUNDING

Innovative Medicines Initiative 2 Joint Undertaking and Coalition for Epidemic Preparedness Innovations.

Urgent considerations for booster vaccination strategies against Ebola virus disease

With two endorsed and prophylactic vaccines against Zaire ebolavirus (referred to hereafter as EBOV), the number of individuals vaccinated against EBOV worldwide is estimated to range between 500 000 and 1 000 000 individuals, increasing with every renewed EBOV threat and vaccination campaign. Therefore, re-exposure of previously vaccinated health-care workers, and possibly community members, could become more frequent. In the absence of long-term data on vaccine efficacy and duration of protection, we urgently need to understand revaccination strategies that could maximise the level of protection. In this Personal View, we highlight the scarcity of available evidence to guide revaccination recommendations for the accumulating groups of previously vaccinated communities or front-line health-care workers that could be redeployed or re-exposed in the next EBOV outbreak(s). This evidence base is crucial to identify optimal target populations and the frequency of booster doses, and guide vaccine interchangeability (especially in settings with limited or unpredictable vaccine supplies), while preventing vaccine mistrust, equity concerns, and exclusion of vulnerable populations. We discuss five priority gaps (to whom, when, and how frequently, to provide booster doses; long-term correlates and thresholds of protection; the effect of vector-directed immunity and viral variant protection; comparative research in mix-and-match schedules; and implementation concerns) that should be urgently tackled to adapt the initial EBOV prophylactic vaccination strategies considering potential booster dose vaccinations.

Protective MVA-ST Vaccination Robustly Activates T Cells and Antibodies in an Aged-Hamster Model for COVID-19

Aging is associated with a decline in immune system functionality. So-called immunosenescence may impair the successful vaccination of elderly people. Thus, improved vaccination strategies also suitable for an aged immune system are required. Modified Vaccinia virus Ankara (MVA) is a highly attenuated and replication-deficient vaccinia virus that has been established as a multipurpose viral vector for vaccine development against various infections. We characterized a recombinant MVA expressing a prefusion-stabilized version of SARS-CoV-2 S protein (MVA-ST) in an aged-hamster model for COVID-19. Intramuscular MVA-ST immunization resulted in protection from disease and severe lung pathology. Importantly, this protection was correlated with a potent activation of SARS-CoV-2 specific T-cells and neutralizing antibodies. Our results suggest that MVA vector vaccines merit further evaluation in preclinical models to contribute to future clinical development as candidate vaccines in elderly people to overcome the limitations of age-dependent immunosenescence.

Modeling Supply and Demand Dynamics of Vaccines against Epidemic-Prone Pathogens: Case Study of Ebola Virus Disease

Health emergencies caused by epidemic-prone pathogens (EPPs) have increased exponentially in recent decades. Although vaccines have proven beneficial, they are unavailable for many pathogens. Furthermore, achieving timely and equitable access to vaccines against EPPs is not trivial. It requires decision-makers to capture numerous interrelated factors across temporal and spatial scales, with significant uncertainties, variability, delays, and feedback loops that give rise to dynamic and unexpected behavior. Therefore, despite progress in filling R&D gaps, the path to licensure and the long-term viability of vaccines against EPPs continues to be unclear. This paper presents a quantitative system dynamics modeling framework to evaluate the long-term sustainability of vaccine supply under different vaccination strategies. Data from both literature and 50 expert interviews are used to model the supply and demand of a prototypical Ebolavirus Zaire (EBOV) vaccine. Specifically, the case study evaluates dynamics associated with proactive vaccination ahead of an outbreak of similar magnitude as the 2018-2020 epidemic in North Kivu, Democratic Republic of the Congo. The scenarios presented demonstrate how uncertainties (e.g., duration of vaccine-induced protection) and design criteria (e.g., priority geographies and groups, target coverage, frequency of boosters) lead to important tradeoffs across policy aims, public health outcomes, and feasibility (e.g., technical, operational, financial). With sufficient context and data, the framework provides a foundation to apply the model to a broad range of additional geographies and priority pathogens. Furthermore, the ability to identify leverage points for long-term preparedness offers directions for further research.