Scientists hail '100% effective' Ebola vaccine

"Ebola vaccine is 'potential game-changer'," says BBC News, while the Daily Mail cites a "100% effective jab" for the disease. These headlines stem from early results of a trial investigating the effects of an Ebola vaccine during the most recent outbreak of the virus in west Africa.

Researchers gave the Ebola virus vaccine to thousands of people in Guinea who'd had close contact with an infected individual – a process called "ring vaccination". Half the sample were given the vaccine immediately, while the other half were given the vaccine after a delay of three weeks.

The early results, published in The Lancet and publicised by the World Health Organization (WHO), showed the vaccine had 100% effectiveness when given immediately. Nobody developed Ebola symptoms up to 10 days after being given the vaccine immediately after exposure. However, 16 cases in the delayed vaccination group developed symptoms (0.5%). Further analysis of the results is ongoing.

The vaccine is not currently licensed for use. The data on its effectiveness and safety will need to be reported and scrutinised before we know whether it could be licensed and widely adopted.

Researchers are now trying the vaccine in Ebola-affected Sierra Leone. Liberia is the only other country affected by the Ebola virus at the moment, according to government information on Ebola. 

What is Ebola?

Ebola is a serious viral infection that can often be fatal. It is spread by close contact with an infected person, particularly through blood and other bodily secretions. For example, someone caring for a person with the Ebola virus could get infected after changing wound dressings or bed pans.

The first symptoms of Ebola virus disease can start anywhere up to three weeks after being infected. Symptoms include fever, headache, sore throat, general fatigue and weakness, muscle pains, vomiting and diarrhoea.

Ebola can also cause internal bleeding, which may present as bruising, a rash, bleeding from the mouth or gums, or blood in the stool. Because of this, the infection is sometimes called Ebola haemorrhagic fever.

There is no specific treatment for Ebola and care is usually supportive – for example, providing intravenous fluids. The average death rate from Ebola is reported to be 50%, though this varies depending on the health and immunity of the person who has been affected. Prevention of Ebola has always been better than cure.

In 2014, the largest known Ebola outbreak in history began in west Africa, centring on Guinea, Liberia and Sierra Leone. There were also individual cases of healthcare workers infected in west Africa who then imported the virus into western countries. No licensed Ebola vaccines were available, but they have been under investigation.  

Why is the Ebola vaccine in the news?

Early results of a phase III trial of the VSV-EBOV vaccine have been published by the WHO, and have also been reported in The Lancet. Phase III means this trial is in one of the final stages of testing the effectiveness and safety of the vaccine in a large sample of people.

The vaccination trial began in Guinea in March 2015 and has involved giving the vaccine to 7,651 volunteers. These are the contacts of people who have been infected with the virus (family members, neighbours, colleagues and so on).

This technique of identifying an infected person, their contacts, and their contacts' contacts is called "ring vaccination". It is said to be based on the strategy used to eradicate smallpox.

Study co-author, John-Arne Røttingen, who is director of the Division of Infectious Disease Control at the Norwegian Institute of Public Health, says: "The premise is that by vaccinating all people who have come into contact with an infected person you create a protective 'ring' and stop the virus from spreading further."

An editorial in The Lancet accompanying the research says the ring vaccination process isn't easy, as it can be hard to identify the network of contacts of a particular person, particularly when family and friends can be in dispersed communities across the country.

Rather than comparing the vaccine with an inactive placebo, roughly half of the contacts in the trial (4,123) were given the vaccine immediately; the remainder (3,528) after a three-week delay.

The ring vaccination trial stopped recruiting in July 2015. Another trial is said to be being conducted in parallel with the trial of ring vaccination, involving vaccinating frontline workers caring for sick people. 

What are the early trial results?

The trial showed 100% effectiveness when given immediately, with no vaccinated cases having Ebola symptoms up to 10 days after the vaccine.

In the delayed vaccination group, there were 16 people who developed Ebola symptoms up to 10 days after infection, affecting 0.5% of those exposed who received delayed vaccination.

All of these cases developed symptoms within one week of exposure to the infected person. The overall vaccine effectiveness in all people who received it is estimated to be around 75%.

As the WHO statement says, better evidence is also needed on the vaccine's capacity to protect the whole population through what is called "herd immunity".

What this means is that if enough people in a population are vaccinated or immune against an infection, this confers protection on unvaccinated people, as there aren't enough people around to catch and spread the virus in the first place.

Side effects were examined up to 12 weeks after vaccination. There were 43 serious side effects reported, one of which was a serious fever attributed to the vaccine. This resolved spontaneously. Assessment of side effects is ongoing. 

What do the results mean at the moment?

The vaccine is not currently licensed for use. More data on its safety and effectiveness is needed before it can be licensed for widespread use, and it will only pass if the evidence is good enough.

However, The Lancet reports background preparation may already be under way for its introduction: "If the evidence proves sufficient for licensing, a Global Ebola Vaccine Implementation Team, also under WHO's leadership, has been preparing the ground for its introduction – creating guidelines for the vaccine's use, strategies for community engagement, and mechanisms to expand country capacity for the vaccine's distribution and delivery."

It is also not possible to say who would be eligible for the vaccine – for example, whether it would just be healthcare workers in affected areas, or those who are known to have come into contact with an infected person.

The news of the successful Ebola vaccine trials has received widespread welcome from scientists. You can read the experts' views on the Ebola vaccine on the Science Media Centre website.