RMS Develops World’s First Probabilistic Model of West African Ebola Outbreak, Finds Current Outbreak Has Potential to be Deadliest Infectious Disease Event in a Century
Current outbreak will worsen and could reach as many as 1,400 new cases per day within a month, according to pandemic risk experts
NEWARK, Calif. -
October 23, 2014 -
to a new report by RMS, the world’s leading catastrophe risk management
firm, the Ebola virus disease outbreak in West Africa has the potential to be
the most deadly infectious disease event since the 1918 flu pandemic.
The current outbreak will continue to worsen while
the deployment of resources is ramped up to meet the caseload. According to RMS
modeling, until a tipping point is reached where the number of new daily cases declines
rather than increases, the severity of the outbreak will continue to multiply, with
the total number of new cases approximately doubling each month.
“Controlling the spread of this Ebola outbreak
is more a question of logistics than virology,” said Dominic Smith, pandemic
risk expert and senior manager of LifeRisks
at RMS. “The fight against the Ebola epidemic is a race against a moving
target; more resources are required as the number of cases increases.”
RMS modeling suggests that, based on current
response efforts, the tipping point will not be reached until January 2015.
Modeling further reveals a 55 percent chance that by the end of November, at
least 1,000 new cases of Ebola will develop daily, and as many as 1,400 per day
in a worst-case scenario. There have been more than 9,000 cases reported in
total to date.
Adding to the devastation of the Ebola outbreak,
overwhelmed medical systems in West Africa have less
resources to respond to other diseases and the mortality rate of
malaria and yellow fever is on the rise. Malaria
deaths are likely to continue rising as the seasonal height of malaria transmission is reached next month.
RMS modeled the future paths of cases and
deaths from the Ebola virus in Sierra Leone, Guinea and Liberia, which were combined
with a probabilistic assessment of various international medical and military
response scenarios to estimate the timing of the tipping point where cases are
controlled such that the disease tapers off.
If effective resources are deployed at a rate
that outstrips the pace of increase in new cases, a tipping point can be
reached where the number of new daily cases reaches a maximum, allowing response
measures to kick in and prevent new infections at a rate that causes the
epidemic to subside.
“The way to stop this outbreak is simple in
principle and has been demonstrated in Nigeria and in specific cities in the
affected region: reduce contacts with infected people by more than half,”
said Smith. “The scale and pace of the international response will define how
long it takes to reach the tipping point.”
The U.S. Centers for Disease Control and
Prevention (CDC) estimates that, even in the absence of treatments and
vaccines, the epidemic would be brought under control and eventually come to an
end if approximately 70 to 75 percent of cases are in medical care or treatment
units, or in environments where there is a reduced risk of disease
In a realistic scenario based on current
response efforts, RMS analysis projects the tipping point will be reached at
the end of January 2015, with the outbreak subsiding by June 2015.
When modeling a disease, RMS first looks at
the reported virulence and the transmissibility of the pathogen
responsible for causing Ebola. This virus is extremely deadly, with an
estimated case fatality rate of 69 to 73 percent. This range of estimates for
transmissibility, as measured by R0,
is between 1.5 and 2.2, which means on average an infected individual will
transmit the virus to approximately two other people in a susceptible
then takes into account mitigating criteria, including medical and non-medical
interventions. In its modeling, RMS evaluated the current response resources in
place in impacted countries, further resources already pledged and a range of
estimates of potential additional resources that will be deployed. For each
country, RMS used these factors to formulate five scenarios, ranging from very
optimistic to very pessimistic, and their associated probabilities.
The number of beds for Ebola treatment
currently in use is far below what is needed to reverse the outbreak in any of
the three effected countries. To reach the tipping point sooner, faster ramp up
of mitigating efforts is essential, but subsequently, fewer total beds and
resources in general will be required.
For example, in order to reach the tipping
point in Sierra Leone, the current number of beds in use needs to be
approximately tripled by the end of November to halt the outbreak with the
smallest total number of cases and at the lowest overall cost. If that fails,
the number will need to increase to six times today’s number by the end of December
to halt the outbreak.
A large degree of reliance will be placed on
beds being rolled out in Ebola treatment centers (ETCs), which cost $5.7
million to set up and run a fifty-bed center for one month. Ebola community
care units (ECUs) staffed by rapidly trained non-experts rather than medical
workers are being set up in some areas, but there is larger uncertainty
surrounding their effectiveness.
Treatments might help reduce the case fatality
rate, but are very unlikely to have a significant role in halting the spread of
the Ebola epidemic. An Ebola vaccine might be available in time to shorten the
epidemic, but will not be produced in sufficient quantities to have an active
role in halting the spread of the epidemic in the next few months.
RMS does not expect this outbreak of Ebola to
become a significant mortality threat in other parts of the world. It is
possible that it could spread to neighboring countries in West Africa. This
risk can be reduced by appropriate screening of people leaving the impacted
region and could be contained with rapid implementation of effective control
In the situation where there are potentially
10,000 new cases per week in West Africa, there will be more cases exported
into other countries. This is possible via two routes:
Foreign workers combating the spread of the virus are likely to be
repatriated to their home countries. Currently the United States, United
Kingdom, France and Cuba have delivered personnel in significant numbers.
RMS does not consider this to be a probable source of escalation as such
cases will be monitored and isolated by the public health systems already
in place in those countries.
Infected people travelling to other regions unchecked could
transmit Ebola outside of West Africa. However, the capability of most
countries to trace contacts ishigher than in Liberia and Sierra
Leone, and stronger travel control measures could be implemented if case
numbers exceeded a prudent limit.
RMS will be updating the model with new numbers every few weeks, projecting the course of the event in near real-time.
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