Understanding Ebola Virus Vaccines: Key Insights on Ervebo and Janssen's New Options for Outbreak Management

Ebola virus disease (EVD) remains a serious public health threat in parts of Africa, with outbreaks causing high mortality and social disruption. Vaccination plays a crucial role in controlling these outbreaks and protecting those at highest risk. Two vaccines have gained approval for Ebola virus prevention: Ervebo, developed by Merck & Co., and the two-dose regimen of Zabdeno and Mvabea by Janssen Pharmaceutica. This post explores these vaccines, their recommended use, access pathways during outbreaks, and ongoing efforts to develop vaccines for other Ebola species.

Ervebo vaccine vial ready for administration during Ebola outbreak

Approved Ebola Vaccines and Their Profiles

Ervebo by Merck & Co.

Ervebo is a single-dose, live-attenuated vaccine designed to protect against the Zaire ebolavirus species, the most common cause of Ebola outbreaks. It uses a recombinant vesicular stomatitis virus (rVSV) platform, where the VSV glycoprotein is replaced with the Ebola virus glycoprotein, triggering a strong immune response.

• Approval: Licensed by the U.S. FDA in 2019 and prequalified by the World Health Organization (WHO).

• Efficacy: Clinical trials and outbreak use have shown Ervebo to be highly effective in preventing Ebola virus disease.

• Use: Administered as a single intramuscular injection.

  
  

Zabdeno and Mvabea by Janssen Pharmaceutica

This vaccine regimen consists of two doses:

• Zabdeno (Ad26.ZEBOV) is the first dose, a non-replicating adenovirus vector vaccine.

• Mvabea (MVA-BN-Filo) is the second dose, given 8 weeks later, using a modified vaccinia Ankara vector.

  
  

This two-dose approach aims to provide durable immunity against the Zaire ebolavirus.

• Approval: Received European Medicines Agency (EMA) approval in 2020.

• Use: Recommended for preventive vaccination, especially for healthcare workers and populations at risk.

  
  

Ervebo’s Role in Outbreak Response and SAGE Recommendations

In July 2024, the WHO’s Strategic Advisory Group of Experts (SAGE) on Immunization updated its recommendations for Ebola vaccines. SAGE strongly supports the use of Ervebo as part of outbreak response strategies. The vaccine is recommended for:

• Ring vaccination around confirmed Ebola cases, targeting contacts and contacts of contacts.

• Frontline healthcare workers and responders in outbreak zones.

• Populations in high-risk areas during active outbreaks.

  
  

SAGE highlights Ervebo’s rapid onset of protection and ease of administration as key factors for outbreak control. The vaccine’s single-dose regimen allows quick deployment and coverage in emergency settings.

Accessing Ervebo During Confirmed Outbreaks

During confirmed Ebola outbreaks, Ervebo vaccines are made available through the International Coordinating Group (ICG) on Vaccine Provision. The ICG is a global mechanism that coordinates vaccine stockpiles and distribution to countries facing outbreaks.

• Countries submit requests to the ICG for emergency vaccine supplies.

• The ICG manages a global stockpile of Ervebo doses, ensuring rapid delivery.

• This system has been critical in recent outbreaks in the Democratic Republic of Congo and West Africa.

  
  

The ICG’s role ensures that vaccines reach affected areas quickly, supporting containment efforts and reducing transmission.

Preventive Vaccination for Healthcare and Frontline Workers via Gavi

Beyond outbreak response, preventive vaccination is essential to protect healthcare workers and frontline responders who face ongoing risk. Gavi, the Vaccine Alliance, supports countries in accessing Ebola vaccines for this purpose.

• Gavi funds and facilitates vaccine procurement and delivery.

• Target groups include healthcare workers in Ebola-prone regions and laboratory personnel.

• Preventive vaccination helps maintain healthcare capacity and reduces the risk of nosocomial transmission.

  
  

This proactive approach complements outbreak response vaccination, building resilience in vulnerable health systems.

Development of Candidate Vaccines for Other Ebola Species

While Ervebo and Janssen’s vaccines target the Zaire ebolavirus, other Ebola species such as Sudan virus disease (SVD) also cause outbreaks. Vaccine development efforts are underway to address these gaps:

• Candidate vaccines for Sudan virus and Bundibugyo virus are in preclinical and clinical trial stages.

• These vaccines use similar viral vector platforms adapted for different Ebola species.

• Expanding vaccine options will improve preparedness for diverse Ebola threats.

  
  
  
  

The CORE Protocol for Evaluating Vaccine Candidates

To accelerate vaccine development and evaluation, the WHO coordinates the CORE (Clinical Outbreak Response and Evaluation) protocol. This standardized framework enables:

• Rapid assessment of vaccine safety and efficacy during outbreaks.

• Comparison of multiple vaccine candidates using consistent methods.

• Collaboration among researchers, governments, and manufacturers.

  
  

The CORE protocol has supported the evaluation of Ervebo and Janssen vaccines and continues to guide testing of new candidates, ensuring timely data to inform public health decisions.

Summary and Next Steps

Vaccination remains a cornerstone in controlling Ebola outbreaks. Ervebo’s single-dose vaccine is the frontline tool for outbreak response, supported by SAGE recommendations and coordinated access through the ICG. Janssen’s two-dose Zabdeno and Mvabea regimen offers an additional preventive option, especially for healthcare workers. Efforts to develop vaccines for other Ebola species and the use of the CORE protocol promise to strengthen global preparedness.

For public health professionals and policymakers, understanding these vaccines and access mechanisms is vital. Supporting vaccination programs, ensuring timely delivery, and investing in new vaccine research will help reduce the impact of Ebola outbreaks and protect vulnerable communities.