Ebola vaccine hope after successful animal study

Dullstroom, in Mpualanga province. Credit: Google Street View

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“Hopes for an effective Ebola vaccine have been raised after trials of an experimental jab found that it gave monkeys long-term protection,” The Guardian reports. An initial animal study found that a new vaccine boosted immunity.

Ebola is an extremely serious and often fatal viral infection thst can cause internal bleeding and organ failure.

It can be spread via contaminated body fluids such as blood and vomit.

Researchers tested vaccines based on chimpanzee viruses, which were genetically modified to not be infectious and to produce proteins normally found in Ebola viruses. As with all vaccines, the aim is to teach the immune system to recognise and attack the Ebola virus if it comes into contact with it again.

They found that a single injection of one form of the vaccine protected macaques (a common type of monkey) against what would usually be a lethal dose of Ebola five weeks later. If they combined this with a second booster injection eight weeks later, then the protection lasted for at least 10 months.

The quest for a vaccine is a matter of urgency, due to the current outbreak of Ebola in West Africa.

Now that these tests have shown promising results, human trials have started in the US. Given the ongoing threat of Ebola, this type of vaccine research is important in finding a way to protect against infection.


The study was carried out by researchers from the National Institutes of Health (NIH) in the US, and other research centres and biotechnology companies in the US, Italy and Switzerland. Some of the authors declared that they claimed intellectual property on gene-based vaccines for the Ebola virus. Some of them were named inventors on patents or patent applications for either chimpanzee adenovirus or filovirus vaccines.

The study was funded by the NIH and was published in the peer-reviewed journal Nature Medicine.

The study was reported accurately by the UK media.


This was animal research that aimed to test whether a new vaccine against the Ebola virus could produce a long-lasting immune response in non-human primates.

The researchers were testing a vaccine based on a chimpanzee virus from the family of viruses that causes the common cold in humans, called adenovirus. The researchers were using the chimpanzee virus rather than the human one, as the chimpanzee virus is not recognised and attacked by the human immune system.

The virus is essentially a way to get the vaccine into the cells, and is genetically engineered to not be able to reproduce itself, and therefore not spread from person to person or through the body. Other studies have tested chimp virus-based vaccines for other conditions in mice, other primates and humans.

To make a vaccine, the virus is genetically engineered to produce certain Ebola virus proteins. The idea is that exposing the body to the virus-based vaccine “teaches” the immune system to recognise, remember and attack these proteins. Later, when the body comes into contact with the Ebola virus, it can then rapidly produce an immune response to it.

This type of research in primates is the last stage before the vaccine is tested in humans. Primates are used in these trials due to their biological similarities to humans. This high level of similarity means that there is less chance of humans reacting differently.


Chimpanzee adenoviruses were genetically engineered to produce either a protein found on the surface of the Zaire form of the Ebola virus, or both this protein and another found on the Sudan form of the Ebola virus. These two forms of the Ebola virus are reported to be responsible for more deaths than other forms of the virus.

They then injected these vaccines into the muscle of crab-eating macaques and looked at whether they produced an immune response when later injected with the Ebola virus. This included looking at which vaccine produced a greater immune response, how long this effect lasted and whether giving a booster injection made the response last longer. The individual experiments used between four and 15 macaques.


In their first experiment, the researchers found that macaques given the vaccines survived when injected with what would normally be a lethal dose of Ebola virus five weeks after vaccination. Using a lower dose protected fewer of the vaccinated macaques.

The vaccine used in these tests was based on a form of the chimpanzee adenovirus called ChAd3. Vaccines based on another form of the virus called ChAd63, or on another type of virus called MVA, did not perform as well at protecting the macaques. A detailed assessment of the macaques' immune responses suggested that this might be due to the ChAd3-based vaccine producing a bigger response in one type of immune system cell (called T-cells).

The researchers then looked at what happened if vaccinated monkeys were given a potentially lethal dose of Ebola virus 10 months after vaccination. They did this with groups of four macaques given different doses and combination of the vaccines against both forms of Ebola virus, given as a single injection or with a booster. They found that a single high-dose vaccination with the ChAd3-based vaccine protected half of the four macaques. All four of the macaques vaccinated survived if they were given an initial vaccination with the ChAd3-based vaccine, followed by an MVA-based booster eight weeks later. Other approaches performed less well.


The researchers concluded that they had shown short-term immunity against Ebola virus could be achieved with a single vaccination in chimps, and also long-term immunity if a booster was given. They state that: “This vaccine will be beneficial for populations at acute risk during natural outbreaks, or others with a potential risk of occupational exposure.”


This study has shown the potential of a new vaccine for Ebola virus in chimpanzees. Interest in the quest for a vaccine is seen as urgent, due to the ongoing outbreak of Ebola in West Africa. Animal studies such as this are needed to ensure that any new vaccines are safe, and that they look like they will have an effect. Macaques were used for this research because they, like humans, are primates  therefore, their responses to the vaccine should be similar to what would be expected in humans.

Now that these tests have shown promising results, the first human trials have started in the US, according to reports by BBC News. These trials will be closely monitored to determine the safety and efficacy of the vaccine in humans as, unfortunately, this early success does not guarantee that it will work in humans. Given the ongoing threat of Ebola, this type of vaccine research is important to protect against infection.

Analysis by Bazian. Edited by NHS ChoicesFollow Behind the Headlines on TwitterJoin the Healthy Evidence forum.

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