October 24, 2014

expert reaction to study modelling Ebola virus transmission in Liberia

Researchers publishing in The Lancet Infectious Diseases journal have modelled the spread of Ebola in Montserrado, Liberia. They put forward the likely effects of different levels of intervention and at different time points, in terms of number of cases averted, in relation to the current healthcare efforts.

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

“I’m afraid this is an example of a study performed in too much haste and with too little attention to the epidemiological data being collected in the field. The work also has significant problems with the methods it used to fit to Ebola data and with some of the assumptions made about the biological properties of the disease. The study concludes that many more hospital beds beyond those pledged by the US are required to control transmission in Montesarrado.

“Fortunately, reality seems to have already made this paper outdated, as the numbers of new cases seem to have plateaued in this area in the last few weeks and may even be declining. It’s too early to say whether the ongoing and intense control efforts in Monrovia have yet achieved control or merely slowed the epidemic, but what is being seen on the ground is clearly incompatible with the results in this paper.”

Dr Thomas House, Mathematics Institute, University of Warwick, said:

“The authors of this study have used well-established methods to predict the most likely course of the Ebola epidemic conditional on different intervention scenarios, which is a valuable contribution since they did not find other modelling studies of this question in a literature search. There is, however, always the concern that standard modelling tools might not be suitable for a wholly new scenario such as the one unfolding at present.

“During this outbreak, we have seen growth rates sometimes much faster than an exponentially growing ‘doubling’ model would predict, and sometimes much slower; no-one is certain why this is, but the broad message that we should intervene early and decisively when confronted with a new outbreak is one of those rare things that all scientists in a field agree on.”

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

“There are so many unknowns in this current outbreak, especially the true number of infected individuals, but despite the uncertainties, this work generates a roadmap highlighting the most effective methods of containment and the impacts of past and future delays on our ability to stop this outbreak.

“The bottom line is that increased treatment centre capacity, together with more rapid case identification, provides the biggest benefit. When the capacity of these is exhausted then deployment of personal protective kits to the wider community can still make a mark.

“Volunteer groups on the ground have been calling for increased international effort for some months now and, whilst recent efforts have increased, the estimates presented show that these latest efforts still fall way short of what is needed.

“What the models clearly show is that as the international community procrastinates, the number of cases continues to grow exponentially and we end up playing a constant game of catch-up.

“Perhaps talk of vaccines and treatments resulted in the international community taking their eye off the ball a little, becoming a little bit complacent. Whilst these new interventions might still play a role in containment – by shielding healthcare workers and epidemiologists deployed in the field or eventually protecting the wide community when sufficient doses and proof of their effectiveness emerge – what this paper perfectly highlights is the need for increased capacity to facilitate the necessary infection prevention and control. ”

Dr Sebastian Taylor, Lecturer, School of International Development, University of East Anglia, said:

“This paper provides timely evidence that the international response to the Ebola outbreak in West Africa remains too slow and is likely to be too small.

“That the proposed number of treatment centre beds is significantly below the projected requirement is alarming in itself. The underlying question, though, is why the infrastructure of Liberia’s health system was so weak in the first place.

“A recent study of living conditions for Liberians in Monrovia reported that the three highest priority needs were for clean water, electricity and healthcare (AOAV, 2011). The failure to ensure those basic necessities, even in the country’s capital city, is the real story behind this outbreak’s unprecedented – and potentially catastrophic – scale.

“In the last decade, less than 2% of international aid dedicated to health in Liberia has been provided for basic health infrastructure, training health workers, and public health education.  Once the current crisis is under control, the international community of donors needs to urgently reconsider how it spends its aid for health. Stronger investments in building basic health capacity in countries like Liberia will be key to containing the risk of similar outbreaks in the future.”

‘Dynamics and control of Ebola virus transmission in Montserrado, Liberia: a mathematical modelling analysis’ by Lewnard et al. will be published in The Lancet Infectious Diseases at 00:01 UK time on Friday 24^th October 2014, which is also when the embargo will lift. 

All our previous output on this subject can be seen at this weblink: http://www.sciencemediacentre.org/ebola-outbreak/

Declared interests

None declared