Highlights
1. The HeV-sG-V vaccine candidate demonstrated a tolerable safety profile across all tested doses, with no serious adverse events reported.
2. A two-dose regimen of 100 μg administered 28 days apart elicited the highest immunogenic response, producing significant neutralizing antibody titers against both the Bangladesh (NiVB) and Malaysia (NiVM) strains.
3. Single-dose administration was found to be insufficiently immunogenic, highlighting the necessity of a prime-boost strategy for achieving potential clinical protection.
4. These findings support the continued development of HeV-sG-V for both reactive outbreak control and long-term preventive immunization in endemic regions.
The Rising Threat of Nipah Virus: A Clinical Imperative
First identified following a devastating outbreak in Malaysia and Singapore in 1999, the Nipah virus (NiV) has emerged as one of the most lethal zoonotic pathogens known to modern medicine. As a member of the Henipavirus genus within the Paramyxoviridae family, NiV is primarily transmitted to humans through direct contact with infected pigs, consumption of raw date palm sap contaminated by fruit bats (Pteropus species), or through human-to-human transmission in healthcare settings.
The clinical presentation of NiV infection is severe, often characterized by rapid-onset acute respiratory distress syndrome (ARDS) and fulminant encephalitis. Mortality rates are alarmingly high, ranging from 40% to 75% depending on the strain and the capacity of the local healthcare infrastructure. Despite its status as a WHO R&D Blueprint priority pathogen, there are currently no approved vaccines or specific therapeutics for human use. The development of a vaccine is therefore not only a scientific challenge but a critical public health necessity to mitigate the risk of future pandemics.
Rationale for the HeV-sG-V Candidate
The vaccine candidate evaluated in this study, HeV-sG-V, is based on a recombinant soluble version of the attachment G glycoprotein of the Hendra virus (HeV). Because HeV and NiV share significant structural and sequence similarities in their attachment glycoproteins, researchers hypothesized that a vaccine targeting the HeV-sG protein could provide heterologous cross-protective immunity. Preclinical studies in non-human primates and other animal models have previously demonstrated that antibodies raised against HeV-sG can effectively neutralize NiV, providing a strong biological rationale for this Phase 1 human trial.
Study Design and Methodology
This Phase 1, single-center, randomized, observer-blind, placebo-controlled study was designed to rigorously evaluate the safety, tolerability, and immunogenicity of HeV-sG-V in a healthy adult population. The trial enrolled 192 participants aged 18–49 years at a facility in the United States. Participants were excluded if they had pre-existing immunological conditions, recent exposure to Henipaviruses, or a history of significant allergies to vaccine components.
Dosing and Randomization
Participants were randomly assigned in a 5:1 ratio to receive either the vaccine or a placebo across three ascending dose cohorts:
1. Cohort 1: 10 μg dose.
2. Cohort 2: 30 μg dose, administered on Day 1 and either Day 8 or Day 29.
3. Cohort 3: 100 μg dose, following the same timing as Cohort 2.
Primary and Secondary Endpoints
The primary focus was on safety, including solicited local and systemic adverse events (AEs), unsolicited AEs, and clinically significant laboratory abnormalities. Secondary endpoints focused on the humoral immune response, specifically serum IgG binding via ELISA and neutralizing antibody responses against prototypical NiV Bangladesh (NiVB) and NiV Malaysia (NiVM) reporter viruses.
Key Findings: Safety and Tolerability
The safety data from the 173 participants who completed the per-protocol criteria were highly encouraging. The most frequently reported adverse event was mild-to-moderate injection site pain, which is consistent with other recombinant protein vaccines utilizing adjuvants. Systemic reactions, such as low-grade fever or malaise, were transient and did not lead to study withdrawal.
Critically, there were no reported serious adverse events (SAEs), hospitalizations, or deaths during the study period. Laboratory monitoring did not reveal any patterns of toxicity or clinically significant deviations from baseline. This tolerable risk profile across all three dose levels suggests that HeV-sG-V is suitable for further clinical advancement in broader populations.
Key Findings: Immunogenicity and Dose-Response Relationship
The immunogenicity results revealed a clear dose-dependent response. A single administration of the vaccine, regardless of the dose level, did not achieve levels of neutralizing antibodies likely to be protective in a clinical setting. This suggests that a prime-dose alone is insufficient to prime the immune system against the complex glycoprotein structure of the virus.
The Advantage of the 100 μg Two-Dose Regimen
The most robust immune responses were observed in Cohort 3, specifically among those who received two 100 μg doses 28 days apart. In this group, neutralizing antibody geometric mean titres (GMTs) rose dramatically seven days after the second dose. The results were as follows:
1. NiV Bangladesh (NiVB): GMT of 1485.6 (95% CI: 990.5–2228.1).
2. NiV Malaysia (NiVM): GMT of 2581.9 (95% CI: 147.1–3194.2).
These results are significant because they demonstrate that the vaccine effectively triggers a memory B-cell response that can be rapidly boosted, producing high-affinity antibodies that neutralize both major geographic variants of the virus.
Expert Commentary: Clinical and Translational Implications
From a clinical perspective, the HeV-sG-V vaccine represents a major milestone in tropical medicine. The ability to induce cross-strain neutralization is particularly vital, as NiV outbreaks in Malaysia often present with different clinical nuances than those in Bangladesh or India. The rapid induction of antibodies within one month of the first dose—provided a second dose is administered—indicates that this vaccine could be deployed as a reactive tool during an active outbreak to create a ring of immunity around confirmed cases.
However, some experts note that while the results are promising, the study was conducted in a healthy, young population in a non-endemic setting. Future research must address whether the vaccine remains equally immunogenic in older adults or immunocompromised individuals, who may be at higher risk during outbreaks. Additionally, the longevity of the antibody response beyond the initial study period remains a key question for determining the frequency of potential booster doses.
Conclusion and Future Directions
This Phase 1 study confirms that HeV-sG-V is a safe and immunogenic candidate for preventing Nipah virus infection. The transition from a single-dose to a two-dose 100 μg regimen appears to be the most viable path forward for Phase 2 trials. As the world continues to face the threat of emerging zoonotic diseases, the development of a stable, effective vaccine against Nipah virus is a paramount priority for global health security.
Funding and Clinical Trial Information
This study was funded by the Coalition for Epidemic Preparedness Innovations (CEPI). ClinicalTrials.gov Identifier: NCT04199169.
References
Frenck RW Jr, Naficy A, Feser J, et al. Safety and immunogenicity of a Nipah virus vaccine (HeV-sG-V) in adults: a single-centre, randomised, observer-blind, placebo-controlled, phase 1 study. Lancet. 2025 Dec 13;406(10521):2792-2803. doi: 10.1016/S0140-6736(25)01390-X.
