select search filters
roundups & rapid reactions
factsheets & briefing notes
before the headlines
Fiona fox's blog

expert reaction to media reports suggesting the Ebola virus may have mutated

Media reports have suggested that the Ebola virus might have mutated, based on comments from scientists at the Institut Pasteur in France.


Prof. Paul Cosford, Director for Health Protection and Medical Director, Public Health England, said:

“Ebola is a type of virus (an RNA containing virus) which we expect to mutate over time. Analysis of Ebola genes will inevitably identify such mutations.

“Currently there is no evidence of mutations leading to people being able to catch Ebola from someone who does not themselves have symptoms of Ebola.  Also, no viruses affecting humans have been known to mutate and change their mode of transmission, so there is no evidence to suggest that Ebola could become airborne.

“Ebola is transmitted by direct contact with the bodily fluids, such as blood, vomit or faeces, of an infected person while they are ill.

“How is the situation being monitored?  It is impossible to predict changes in the transmission and severity of Ebola virus infections based on genetic information alone.

“Continued, detailed surveillance of people with Ebola and their contacts in West Africa, and linking this to information on gene sequences is needed to monitor links between any mutations and changes to the transmission and severity of Ebola infection.

“Would a mutated strain affect the way we detect Ebola in the UK?  No. The testing schedule employed in PHE includes a panel of tests, one of which is a pan-ebolavirus assay designed to pick up all variants of Ebola viruses.  This alone renders it most unlikely that viral mutation would prevent detection.”



Dr Peter Walsh, Division of Biological Anthropology, University of Cambridge, said:

“Although case fatalities rates appear to have dropped during the outbreak, no data or analyses have been published rigorously linking this to reductions in virulence. The fatality decrease could just as easily be associated with improved care or reporting problems. Likewise, no robust evidence has been published demonstrating increases in transmissibility.

“After some notable efforts at open data sharing early in the outbreak, the publication of viral genetic data has completely dried up. These data are absolutely critical to assessing whether the virus is evolving towards greater transmissibility, whether vaccines and treatments are likely to be effective, and many other important questions. The more people who seek to answer the questions, the more likely they will be answered quickly and decisively.”


Dr Emma Thompson, Clinical Senior Lecturer and Consultant in Infectious Diseases, MRC-University of Glasgow Centre for Virus Research, said:

“Most RNA viruses have high mutation rates and Ebola virus is no exception. Viral mutation often results in strains less able to replicate than the original strain (negative selection), may have no effect at all (neutral selection) or may allow the virus to transmit more readily or to escape from the immune response or treatment (a phenomenon called positive selection) – this shape-shifting ability is a concern but there is no definite evidence at present that Ebola has mutated to become more transmissible or less likely to be targeted by the immune response following vaccination. Comparison of the genetic data from strains that are now circulating with those used in vaccines combined with laboratory-based research looking at the functional immune response in patients who have been vaccinated to these mutated strains would help scientists to determine the likelihood of vaccine failure in the future. Any association between transmissibility or disease severity and changes in viral strains will require a very detailed and rigorous epidemiological study – a major challenge during a public health emergency.

“It is essential that all authors publishing results of genetic analysis of Ebola virus upload the data to public databases in order to facilitate timely analysis to be carried out by multiple laboratories (journals should insist on this) – a collaborative approach will allow more rapid analysis and could save lives.”


Prof. Paul Hunter, Professor of Health Protection, University of East Anglia (UEA), said:

“I think it would be premature to suggest that apparent asymptomatic infections and reduced case fatality rate are due to the virus becoming less virulent and more transmissible.

“The issue of asymptomatic infections is not new, as seropositive people have been described in several prior papers. For example, as long ago as 1981 in the DRC, Jezek et al. (1999) showed that of 188 contacts of 30 Ebola cases, 28 (15%) had high antibody levels to Ebola and of these only four had symptoms consistent with a clinical diagnosis of Ebola. So asymptomatic infection may have always been quite common without mutating virus having been the cause.

“Any decline in case fatality rate could well be explained by improved delivery of care later in the outbreak, and by inadequate reporting of continued cases.

“But, we don’t know whether changes in the virus could indeed be changing death rate, because we haven’t yet seen data. It would be tragic if, during a crisis like this, data was not being adequately shared with the public health community. The rapid sharing of data could help enable more rapid control of the outbreak.”


Dr Peter Horby, Senior Clinical Research Fellow, Centre of Tropical Medicine and Global Health, University of Oxford, said:

“The reducing number of cases is allowing much more aggressive supportive care and it is clear that there is a subset of patients who cannot be saved even by quite intensive supportive care in the West Africa context – i.e. careful electrolyte based fluid management. The size of that subset is unclear, but is certainly not rare. So I do think there is a floor to the case fertility rate that could be achievable with aggressive but simple supportive care.”


Prof. Neil Ferguson, Professor of Mathematical Biology, Imperial College London, said:

“There’s no robust evidence that the case fatality rate has changed very much over the course of the epidemic. The apparent changes seen are likely mostly an artefact of the challenges in tracking the epidemic. The clinical outcomes of a large proportion of Ebola cases are not being followed-up (or at least reported) after cases are initially detected. This means the public statistics on Ebola deaths substantially underestimate the true number. If one looks at data for the subset of cases where final clinical outcome has been recorded in the Ebola case databases, the case fatality rate has been in the 60-80% range throughout the epidemic. This agrees with what organisations like MSF have seen on the ground in their treatment units.

“It’s important for people to be aware that viruses like Ebola (so-called RNA viruses) accumulate mutations all the time. Mostly those mutations have little or no effect on the characteristics of the disease. At the moment, while we know the virus has mutated during the epidemic (as expected), we have little or no evidence to suggest that there has been any evolutionary adaptation of the virus, for instance which might change transmissibility or lethality. In particular, there is very limited evidence to support the idea that there is any significant level of asymptomatic infection.

“One lesson to be learned from the current Ebola epidemic is the need for more timely collection and sharing of genetic data from virus samples gathered during major outbreaks. Disappointingly, very little genetic data has been released during the current epidemic. Had genetic data been more rapidly generated and then shared, we would know much more about the evolution of the Ebola virus than we do now.”


Dr Jimmy Whitworth, Head of Population Health, Wellcome Trust, said:

“The case fatality rate (the proportion of people that die from Ebola once they have become infected) does seem to have dropped substantially at least in some places in west Africa. Here at some individual treatment centres in Freetown and the surrounding areas, the rate appeared to decrease by half between October / November 2014 and December 2014 / January 2015.

“Whether these falls in fatality rate are due to better care, more prompt patient presentation, the virus becoming less virulent, or other reasons is not at all clear – so, even if this virus is mutating (which isn’t unusual in prolonged outbreaks like this), we don’t know whether that is the reason for the drop in deaths.”


Dr Marta Tufet, Science Portfolio Developer at the Wellcome Trust, said:

“The news that the Ebola virus is mutating is not surprising. The longer a virus remains in a human population, the more likely it is to mutate and adapt to its environment. We cannot predict how it will evolve, but there is really no precedent for any known RNA virus to mutate so radically that it would change its mode of transmission. HIV is another RNA virus that mutates all the time and has been circulating in far more people than Ebola, yet its route of transmission remains unchanged.

“It’s important to study how the Ebola virus is changing over time if we are to understand how to tackle it and how it will respond to vaccines and drugs, but comments suggesting the risk is that Ebola will become airborne are unfounded and risk distracting from the important issues at hand.”


Prof. Jonathan Ball, Professor of Molecular Virology, University of Nottingham, said:

“It would be interesting to see the data, but this doesn’t seem to have been published yet.

“We know that viruses mutate, and when a virus is introduced into a new host, and then undergoes continued transmission within that new host, we would expect the virus to adapt to its new host and its new lifestyle.

“Even if the virus is mutating, we don’t know what impact, if any, those genetic changes are having. Asymptomatic infection is not a new thing, it’s been seen in past outbreaks. Why some people remain well whilst others die is not clear, but it’s most likely down to the host; our own genetic make-up has a massive influence on how viral infections affect us.

“Sure, it’s feasible that some of the viral genetic changes might change the severity of the infection, by make the virus less (or even more) dangerous. This wouldn’t be a new thing, and if it is happening it can impact on how we track and locate infections.

“But the truth is, we don’t know the answers. That’s why studying virus and host genetics is important. When at last we have those answers, then we can start to determine their possible impact.”


Declared interests

None declared


All our previous output on this subject can be seen at this weblink:

in this section

filter RoundUps by year

search by tag