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Home / Healthcare & Medicine / Ebola in Context: Understanding Transmission, Response and Control / Potential new treatments
Potential new treatments
Potential new treatments
PETER SMITH: We don’t really know why some patients survive Ebola and some die of it. But we know that there’s a battle essentially between the virus and the body’s immune response. And sometimes the body’s immune response wins. And so people who mount a strong immune response and defeat the virus, they tend to be the ones that survive. And they have antibodies in their blood after they’ve recovered from the infection. So the idea is that if you can actually boost the response of patients who have the disease with antibodies from patients who have recovered, that may help the survival of patients who are suffering from Ebola. It’s been used a little bit before.
We’ve never had an epidemic like this before with respect to Ebola. So it’s not been used on a lot of Ebola patients. But it has been used for some other infections. There is one experience with Ebola, in a previous small epidemic of Ebola, where eight patients were treated with convalescent blood. That’s the blood from patients who had survived Ebola. And of those eight patients, seven survived. Now that sounds very good and was very good. But the problem was they had lots of other interventions as well. And it’s difficult to know whether it was actually the convalescent blood that was responsible for their survival, or whether it was the other interventions, supportive care, that was responsible.
So that’s really why we want to do this study, to really try and see if it does improve survival. There is doubt about whether it’s going to work. And although WHO have recommended this, it’s not a straightforward procedure. There are two basic things one can do. One can either use the blood of convalescent patients, patients who have recovered from Ebola, and transfuse that into affected patients. That’s quite complicated to organise. Takes a long time to transfuse the blood. A better procedure is just to try and extract the plasma. That’s the fraction of blood that contains the antibodies from the survivors, Ebola patients, and use that as therapy in patients.
The problem with that is it’s quite a complicated procedure to extract that plasma. But now devices, small machines, have been developed which, it seems, can be taken to the field. And rather than being confined to large centres, they can actually be used quite close to where patients are being treated. There are risks. There are risks with any intervention. Everything is done to minimise those risks. If you take somebody’s blood or plasma, there’s the possibility that they have other viral infections that might be transmitted through that. There are quite stringent procedures in place to try and minimise those risks. Patients are screened for hepatitis B, for HIV infection, hepatitis C.
And some of the procedures that actually are used in the extraction of plasma do kill viruses. So the risks are not zero, but they’re small. First of all, you have to persuade survivors that they should donate plasma. This involves essentially hooking themselves up to a machine, having blood pass through a machine, the plasma, the antibodies are taken out, and the other blood components go back into the individual. So you have to persuade sufficient numbers of individuals that they wish to volunteer in this way. Initial indications where we’re doing this study in Guinea is that survivors of Ebola are indeed prepared to volunteer in this way. So we’re quite hopeful that there will be a good supply of volunteers.
There then has to be matching of the plasma donation to the individual patients. Not all patients can have all plasma. And then the plasma has to be transfused into the patients into the difficult treatment conditions that are present for the treatment of Ebola. So it is not a straightforward procedure. So it is important to do this trial to see if it works. Because if it doesn’t work, then a lot of time and effort will be saved in not really using this in the future if we can find no evidence that it improves survival. How we’ll be actually testing the therapy is evolving. And it’s dependent to some extent on the supply of material, of either convalescent blood or convalescent plasma.
We had anticipated initially that it would take some time to set up these mobile plasma extraction procedures. And so we were going to start the trial using convalescent blood. And that’s quite a complicated procedure to transfuse. We envisaged we wouldn’t be able to transfuse very many patients, initially at least. And so we could compare the survival of those who were transfused with those who were not transfused. More recently, it’s become apparent that plasma is likely to become more available more quickly. And so we may, as it were, bypass the convalescent blood stage and go straight to the plasma. And that may be available in greater supply so we can give plasma to more patients.
But there probably won’t be enough to treat all patients. And so we will have some patients who are treated and some who are not, and we will compare the survival of those two groups. Ideally, what one would like to do in these circumstances is, as it were, to randomise that some patients receive the plasma and some patients don’t. But the practicalities of doing this in the circumstances in which treatment is being administered are such that our belief is that’s probably not going to be possible.
At the time of writing, the treatment of Ebola is based on supportive care and symptom relief. Experimental therapies are in trials and the position is changing fast. In the video Professor Peter Smith discusses the rationale and plans for testing convalescent plasma as a therapy. In this step we consider the issues and constraints in evaluating this and other new treatments. Early work in new therapies and vaccines for Ebola predated the 2014 outbreak and was done in response to a perceived threat of Ebola as a biological weapon. No new drug or vaccine candidates were taken as far as human trials. With the 2014 outbreak the need to accelerate production and testing of these candidates was realised. In a statement, an ethics panel at the World Health Organization (WHO) agreed that “In the particular circumstances of this outbreak, and provided certain conditions are met, the panel reached consensus that it is ethical to offer unproven interventions with as yet unknown efficacy and adverse effects, as potential treatment or prevention.’1The need for improvements in supportive therapy was discussed in the ‘Research priorities’ step. This step concentrates on new therapies.
Possible therapies
There are broadly three categories of therapy:1) Convalescent blood or plasma2) Antiviral drugs that are already available3) New productsTesting new treatments
The usual process in testing potential new treatments is as follows:2- Animal testing. Consideration of the results and formal approval is required before moving to human testing.
- Testing in (typically 20-80) healthy human volunteers (Phase 1). This is to check for safety, measure side effects and refine the dosage.
- Preliminary testing in individuals with the disease (Phase 2). This is usually done as a randomised controlled trial and gives early, preliminary data on effectiveness and information on safety and side-effects in those with the disease. The numbers of individuals in these trials are usually too small to be sure about effectiveness, although ‘Phase 2B’ trials try to achieve this.
- If Phase 2 studies suggest the new treatment may be effective, Phase 3 trials are conducted. These should include large enough numbers of individuals to get a clear answer on the drug’s effectiveness compared to previous treatments (or a placebo if there are no previous treatments). Safety and side-effects are closely monitored. Results from Phase 3 trials are usually needed for applications for formal approval of the treatment.
- After licensing it is important to continue to monitor the effectiveness and long-term side-effects on larger numbers of patients (Phase 4).
Practical issues when planning trials for the Ebola outbreak include:
- There are few Ebola treatment sites with adequate facilities to support a clinical trial.
- Trials require data collection but data collection is difficult in the high risk areas because of the limited time and difficulties of recording information while wearing personal protective equipment, and because it is difficult to transfer data out of these areas. This further limits the number of suitable sites.
- The number of potential therapies for Ebola is larger than the number of suitable trial sites, so priorities for testing need to be agreed centrally. It is important to keep a database of negative results to counter false claims of efficacy.
- The baseline standard of care and the case fatality rates vary between and within treatment units. For non-randomised trials, sites with uniform and stable baseline standards of care would be needed.
- The case numbers vary drastically over time and place, so it is difficult to predict which units will have enough patients for a trial but not be completely overburdened and unable to conduct a trial safely.
- It is essential that trials do not interfere with routine care. However, in other settings it is often found that the protocols required by trials actually improve routine care.
- ‘compassionate’ use vs product licensure.
- rapid access vs data to demonstrate safety and efficacy.
- randomised controlled trials vs alternative trial designs.
- maintaining public trust.
First trials of therapies for Ebola
The first trials are with convalescent plasma, and two existing antiviral drugs, favipivavir and brincidofovir, all in collaboration with Médecins Sans Frontières (MSF)-run Ebola Treatment Units.3As discussed in the video, there are good theoretical reasons to believe that convalescent plasma could be helpful, and very limited evidence from earlier outbreaks. Given the scale of the current outbreak there are many survivors who can donate plasma, and they have proven willing. Plasma donation may also help to reduce the stigma that surrounds survivors. The first non-randomised trial started in Conakry, Guinea, led by the Antwerp Institute of Tropical Medicine.3Favipiravir has been approved in Japan against influenza (in specific circumstances), has been used in 1000 people and has a good safety profile (although it should not be used in pregnant women because of a risk of birth defects). It was effective in mouse studies of Ebola but not in non-human primates. Large numbers of doses are available. It is being tested in Guéckédou, Guinea, led by the French biomedical research agency, INSERM.3 Preliminary results were presented at the CROI conference in February 2015. These were inconclusive: patients with high viral loads continued to have high mortality. Those with lower viral loads had lower mortality than measured previously, but this was not a randomised comparison and it is not clear if the difference is due to the drug.Brincidofovir was developed as a broad spectrum anti-viral drug. It has been used to treat over 1000 patients with viral diseases, including studies for the treatment of cytomegalovirus and adenovirus. It was being tested in Liberia, in a study led by the University of Oxford.3 But the trial was stopped in February 2015 after recruiting only a few patients, when the incidence of Ebola had declined in Liberia: following discussions with the US Food and Drug Administration (FDA), the pharmaceutical company Chimerix, which manufactures brincidofovir, unexpectedly announced that it would cease to participate in any current or future trials of brincidofovir for Ebola.Other existing therapies:
Interferon is licensed for treatment of hepatitis and multiple sclerosis and is available. It caused a delayed time to death in non-human primates with Ebola, but had no impact on the case fatality rate. Side effects occur and the benefit to risk ratio is unknown.New therapies
Monoclonal antibodies (including ZMapp, made by MappBio, USA,which was used in 7 Ebola patients early in the epidemic) and other potential new therapies are all only available in very small quantities. ZMapp production is being scaled up, and NIH announced plans for a trial of ZMapp in February 2015.TKM-Ebola, made by Tekmira Pharmaceuticals, Canada consists of small interferring RNA which targets genes in Ebola RNA once inside the cell, blocking replication. It is sequence-specific to the current strain of Ebola. A phase II trial started in Sierra Leone in March. It is not placebo controlled, but in practice it is unlikely that all the patients in the treatment centre will receive it, as it is complex to give: it requires slow intravenous infusion each day for a week, and close monitoring of the patients afterwards.There are some candidate therapeutics that have been through Phase 1 trials, while others are at an earlier stage.The latest information is available on the WHO website.As WHO states, ‘[..] [I]t should be noted that the potential compassionate use and further investigation of these compounds should not detract attention from the implementation of effective clinical care, rigorous standards of practice in infection prevention and control… careful contact tracing and follow-up, effective risk communication, and social mobilization, which will be crucial to terminate the epidemic.’4This article is from the online course:
Ebola in Context: Understanding Transmission, Response and Control
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Ebola in Context: Understanding Transmission, Response and Control
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