Ebola: how a vaccine turned a terrifying virus into a preventable disease

The Ebola virus devastated west Africa in 2014, claiming over 11,000 lives in Sierra Leone, Liberia and Guinea.

It was the largest Ebola outbreak since the virus had first been discovered in the Democratic Republic of Congo in 1976.

Ebola is a terrifying virus which, if left untreated, causes bleeding inside the body and through the eyes, nose, mouth and rectum.

Case fatality rates have varied from 25% to 90% in past outbreaks, depending on circumstances and the response.

The 2014 outbreak in west Africa exposed a critical gap in global preparedness for infectious diseases: the absence of effective vaccines.

There were no drugs or vaccines approved to treat or prevent Ebola or ready to enter into clinical trials at the outset of the epidemic. Therefore, many felt it was ethically necessary to conduct such research as quickly and safely as possible.

As a biologist and epidemiologist, I travelled to Guinea amid the chaos to coordinate the laboratory activities of the rVSV-ZEBOV Ebola vaccine trials.

Almost 10,000 participants were enrolled in trials to make sure the drug was safe and effective to use. The trials would last two years and involved more than 500 scientists and healthcare workers.

My five-year-old daughter, Ashanti, spoke words that strengthened my resolve: “People need you to support them. If you don’t go, who will?”

Her encouragement fuelled me as I led the trial’s laboratory operations, navigating immense logistical and emotional challenges.

We had to set up a full laboratory in a week, to process thousands of samples. Delivering the vaccine required ultra cold freezers (minus 80°C); none were available in the country.

We had to address vaccine hesitancy among the population of Guinea, including the medical and academic community.

Of course there was also fear of getting infected by a disease that was a virtual death sentence.

First line workers and individuals in close contact with confirmed Ebola cases were vaccinated with rVSV-ZEBOV. This created a protective “ring” around the infected.

As a field coordinator, I witnessed firsthand the challenges of conducting research into the safety of the vaccine in the middle of an outbreak.

Collaboration between the World Health Organization, Médecins Sans Frontières, the medical research centre Epicentre and local health authorities proved pivotal.

These efforts also underscored the importance of adaptable, rapid-response research during health crises.

On 18 August 2015 the preliminary results of the trial were announced. They marked a turning point in the fight against Ebola. The vaccine’s near-perfect efficacy offered a rare moment of hope.

Today Sierra Leone is embarking on a nationwide campaign with the rVSV-ZEBOV vaccine, trademarked as Ervebo.

The campaign will target 20,000 frontline workers in 16 districts. These include healthcare workers, traditional healers, community health and social workers, laboratory personnel, motorcycle taxi drivers and security forces. Anybody who will be involved in any response to future outbreaks.

How does Ervebo work?

The Ervebo vaccine, developed by Merck, is a single-dose vaccine. It works by using a modified virus to produce antibodies against Ebola, equipping the immune system to recognise and neutralise the virus upon exposure.

Clinical trials have shown its efficacy exceeds 95% in preventing infection from the Zaire Ebola virus strain, the deadliest variant.

The vaccine was deployed during the 2018-2020 Ebola epidemic in the Democratic Republic of Congo under emergency use authorisation.

This allows a medical product to be used without being authorised by the relevant drug agencies, such the Food and Drug Administration in the United States, the European Medicines Agency and the African Medicines Agency.

It was also used in Burundi, Uganda, South Sudan and Rwanda in preventive vaccination campaigns to protect healthcare and frontline workers.

Ervebo is now a cornerstone in the fight against Ebola, particularly in controlling outbreaks caused by the Zaire strain.

However, its success depends on ensuring equitable access and strengthening healthcare systems.

What are the challenges?

Challenges do persist, including limited vaccine supply, logistical hurdles in remote regions, and vaccine hesitancy fuelled by misinformation.

Addressing these obstacles requires coordinated efforts between governments, health organisations and communities.

Additionally, establishing local vaccine manufacturing in Africa should be a long-term goal, giving affected countries greater control over supply and distribution.

Could the vaccine bring an end to Ebola?

While Ervebo is a monumental achievement, it cannot end Ebola on its own.

The virus’s ability to persist in animal reservoirs such as bats and to then be transmitted to humans means that vaccination must be part of a broader strategy.

Integrating vaccination, surveillance, outbreak response and community engagement is essential for achieving long-term control.

Ervebo’s success provides a model for addressing other infectious disease outbreaks, like mpox. Clinical trials during the mpox outbreak could potentially lead to new and effective vaccines.