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Updated April 27, 2017
Infectious Diseases Outbreaks: Yellow Fever in Central Africa
Introduction
victims often develop fever, nausea, muscle pain, and
Since 1980, emerging infectious diseases (EID) have
vomiting. In most instances, related symptoms resolve
resulted in more frequent outbreaks that are causing higher
within four days. According to the CDC, roughly 15% of
numbers of human infections. EID are either new diseases
those who contract yellow fever develop severe symptoms,
or existing ones that have emerged in new areas. In recent
including organ failure. The “yellow” in the name of the
decades, new EID have included Severe Acute Respiratory
disease refers to the jaundice—yellowing of the skin and
Syndrome (SARS) and HIV/AIDS. EID that have spread to
whites of the eyes, often indicating liver damage—that
new geographical areas have included yellow fever and
typically occurs among severe cases. About half of those
Zika. Zoonotic pathogens (organisms that spread from
who experience severe yellow fever die within 10 days.
animals to humans, often through a vector like a mosquito)
While specific treatment for the virus does not exist, yellow
sicken some 1 billion people annually, roughly 15 million
fever can be prevented through vaccination. Eradication is
of whom die. Notable EID outbreaks caused by zoonotic
not considered feasible, as the disease is also found in
pathogens include SARS (2003), Avian Influenza H5N1
primates, from which mosquitos can transmit the disease to
(2005), Pandemic Influenza H1N1 (2009), Middle East
humans.
Respiratory Syndrome coronavirus (MERS-CoV, 2013),
West Africa Ebola (2014), Zika (2015), and Central Africa
Yellow Fever Outbreak in Central Africa
Yellow Fever (2016) and South America Yellow Fever
Insufficient laboratory capacity in many of the areas where
(2016-2017).
the disease is endemic and parallel symptoms caused by
other common tropical diseases (e.g., malaria, dengue, and
On average, Congress has provided about $130 million
other hemorrhagic fevers) have limited the ability to
annually through regular appropriations to the U.S. Agency
estimate the annual cases and deaths. A modelling study
for International Development (USAID) and the U.S.
conducted in 2013 estimated that 84,000-170,000 cases
Centers for Disease Control and Prevention (CDC) for
occurred in Africa during that year, including 29,000-
global pandemic preparedness efforts. Emergency
60,000 deaths.
responses to EID outbreaks have varied, however, but tend
to follow introduction of the disease into the United States.
Angolan health officials reported a yellow fever outbreak to
For example, the 114th Congress appropriated roughly $5
the World Health Organization (WHO) in January 2016.
billion and $2 billion to help control the West Africa Ebola
Yellow fever is endemic in Angola, but this was the first
and Zika outbreaks, respectively, but other Congresses did
large-scale outbreak in 28 years. The last outbreak in the
not provide funds to address SARS or yellow fever
country occurred in 1988, with 37 cases and 14 deaths.
outbreaks. Due to the unpredictable nature of EID
Laboratory tests confirmed yellow fever among 884 of
outbreaks, some question whether Congress will continue to
4,347 samples collected between December 5, 2015, and
emphasize infectious diseases that reach the U.S. shores or
October 20, 2016. Laboratory tests also indicated that 121
whether the 115th Congress might develop a more proactive
of 377 suspected deaths were caused by yellow fever.
approach.
The disease has spread from Angola to several countries,
In January 2016, a yellow fever outbreak in Central Africa
including Brazil, China, the Democratic Republic of Congo
emerged in an urban area for the first time. It overwhelmed
(DRC), and Kenya. The imported yellow fever cases in
the capacity of the affected countries and subsequently
China and Kenya (11 and 2 cases, respectively) were
caused an unprecedented number of illnesses and deaths.
quickly detected and did not spread further. In Brazil and
EID outbreaks are revealing not only the threat that weak
the DRC, however, imported cases led to additional
health systems in developing countries pose to the world,
infections. Scientists are working to control the yellow
but also are elucidating gaps in international frameworks
fever outbreak in Brazil and have contained it in the DRC.
for responding to global health crises. The central Africa
Laboratory tests were conducted on 2,800 samples and
yellow fever outbreak raises questions about what role the
indicated that 78 yellow fever cases, including 16 deaths,
United States might play in addressing infectious disease
had occurred in the DRC from January 1 through October
outbreaks that are occurring at greater frequency and are
26, 2016. WHO reported that 57 of the cases in the DRC
threatening U.S. health security.
were related to the Angola outbreak.
Background on Yellow Fever
International Response
Yellow fever is a disease transmitted by mosquitoes
The unprecedented size of the central African yellow fever
endemic in 47 countries across sub-Saharan Africa (SSA)
outbreak has raised concern among the international
and South America (see Figure 1). Roughly 90% of annual
community about the pace at which EID outbreaks are
yellow fever cases occur in SSA. Many who contract the
occurring and overrunning global response structures.
virus do not exhibit symptoms. Among symptomatic cases,
WHO Director-General Margaret Chan convened an
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Infectious Diseases Outbreaks: Yellow Fever in Central Africa
Emergency Committee meeting in May 2016 to discuss the
Outlook
yellow fever outbreak. She was particularly concerned
The accelerated pace at which EID outbreaks are occurring
about the urban spread of the disease (a first for Angola)
has overwhelmed international health networks and is
and the risk of further spread across the region and the
raising questions about how the United States and other
world. The committee concluded that the outbreak did not
countries can address this challenge. The mass vaccination
“constitute a Public Health Emergency of International
campaign to stop the central African yellow fever outbreak
Concern but is a serious public health event which warrants
became the largest such effort in recent history, and trends
intensified national action with international support.”
indicate that other EID might require similar unprecedented
responses. Issues raised by the outbreak include the
Infectious disease outbreaks in urban areas are a growing
following:
problem that is overwhelming long-standing international
Global Risks—Is the global risk of future yellow fever
stopgap measures. For example, the WHO and several
outbreaks increasing? WHO warns that the global risk
international organizations created the International
of future yellow fever outbreaks is heightened by
Coordination Group on the Provision of Vaccines in 1997
climate change, increased international trade and travel,
to manage the production and distribution of vaccine
and the resurgence of the Aedes aegypti mosquito
stockpiles for cholera, meningitis, and yellow fever. The
(which can spread other tropical diseases, including
stockpile was created to avert the spread of deadly
chikungunya, dengue, and Zika).
infectious disease outbreaks from countries without
International Preparedness—Is the international
sufficient capacity to control them. In recent years,
community prepared to control additional EID
however, mosquito-borne outbreaks, including yellow
outbreaks? Many poor countries lack the ability to
fever, have taxed the global vaccine stockpile, even
detect, prevent, and contain infectious disease outbreaks,
depleting it twice in 2016. A Brazilian manufacturer (Bio-
potentially exacerbating the reach of such outbreaks.
Manguinhos) sent additional yellow fever vaccine doses to
Escalating urbanization further complicates efforts to
supplement the depleted stockpiles.
control infectious disease threats, as curbing disease
outbreaks in dense, urban areas is time- and resource-
Yellow fever vaccine shortages forced WHO to employ a
intensive. For example, more than 41,000 volunteers
fractional dosing campaign, which used one-fifth of the
and 8,000 vaccination teams were enrolled to vaccinate
standard yellow fever vaccine dose. Experts hoped that
some 30 million people against yellow fever in Angola,
fractional dosing would provide sufficient protection to stop
the DRC, and Uganda.
the spread of the diseases and last for at least one year. The
strategy effectively controlled the outbreak, with Angola
Congressional Response—What approach might the
and the DRC having declared the outbreak over in
115th Congress consider going forward? Some groups
December 2016 and February 2017, respectively. Experts
advocate for deepening investments in global health
caution, however, that the region remains vulnerable to
system strengthening efforts worldwide, arguing that
future outbreaks because the disease is endemic to the area.
emergency responses require considerably more
WHO warns that detection of future outbreaks may be
resources than preventive measures and that ignoring
delayed by persistent deficiencies in disease surveillance
poor health conditions worldwide imperils global and
and laboratory capacities in both countries.
domestic security. Others express concern about how
broad-based health systems support could be adequately
measured and monitored.
Figure 1. Areas at Risk of Yellow Fever Transmission: Sub-Saharan Africa and South America
Source: Adapted by CRS from CDC webpage on Yellow Fever at https://www.cdc.gov/yellowfever/, accessed on January 27, 2017.
Notes: Data for sub-Saharan Africa and Latin America were developed in July 2015 and March 2014, respectively.
IF10603
Tiaji Salaam-Blyther, Specialist in Global Health
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Infectious Diseases Outbreaks: Yellow Fever in Central Africa
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