Yellow fever is a disease transmitted by mosquitoes endemic in 47 countries across sub-Saharan Africa and South America (see Figure 1). Roughly 90% of annual yellow fever cases typically occur in sub-Saharan Africa. An ongoing yellow fever outbreak in Brazil and the re-emergence of the disease across South America is the latest event highlighting the global threat of emerging infectious diseases (EID). All of the countries in South America that detected cases in 2016 (Bolivia, Brazil, Colombia, Ecuador, Peru, and Suriname) have contained the outbreaks except Brazil. As of May 4, 2017, Brazil has detected 729 cases and was investigating an additional 663 cases. Of the confirmed cases, 249 died and an additional 45 deaths were under investigation.
EID are either new diseases or existing ones that emerge in new areas. New EID include Severe Acute Respiratory Syndrome (SARS) and HIV/AIDS. EID that have spread to new geographical areas include yellow fever and Zika. Notable EID outbreaks caused by zoonotic pathogens include SARS (2003), Avian Influenza H5N1 (2005), Pandemic Influenza H1N1 (2009), Middle East Respiratory Syndrome coronavirus (MERS-CoV, 2013), West Africa Ebola (2014), Zika (2015), and Yellow Fever (2016).
Some observers assert the United States is vulnerable to yellow fever importation and are concerned about possible shortages of the vaccine. Importation of the disease into Brazil from Angola and the frequency at which the disease and other EID outbreaks are spreading globally have sparked further concern.
Source: Adapted by CRS from CDC, accessed on January 27, 2017.
Notes: Data for Latin America and sub-Saharan Africa were developed in March 2014 and July 2015, respectively.
In Brazil, most human yellow fever cases are occurring in the southeastern part of the country, where most people had not been vaccinated since the region was not considered at risk of yellow fever (as indicated in blue in Figure 1). Most cases are in the states of Minas Gerais (484 confirmed cases and 224 cases under investigation) and Espirito Santo (212 confirmed cases and 306 cases under investigation, see Figure 2). The World Health Organization (WHO) recommends that at least 80% of a population be vaccinated to prevent outbreaks. By the end of 2015, roughly 46% of all Brazilians had been vaccinated, though almost all residents in areas "at risk" had been vaccinated. Brazil purchased roughly 24 million vaccine doses for the southeast region. As of the end of April 2017, about one-third of districts in the region had vaccinated at least 95% of their population.
Over 80% of yellow fever cases in Brazil are men, primarily of working age, who are vulnerable due to their work (such as mining) that may place them in contact with infected primates. Since the outbreak began through May 4, 2017, 3,660 primate deaths have been reported. Tests confirmed that 474 of the deaths were caused by yellow fever, 1,491 deaths are under investigation, and yellow fever was ruled out as the cause of 96 deaths. Reports are emerging of people attacking primates due to fears that they are spreading yellow fever. Scientists assert that primate survival is further threatened by deforestation, which shrinks the number of animals who may act as hosts for diseases and increases susceptibility to disease.
On average, Congress provides some $130 million annually through State-Foreign Operations and Labor-HHS appropriations to the U.S. Agency for International Development (USAID) and the U.S. Centers for Disease Control and Prevention (CDC) to prevent and respond to global EID. Emergency responses to EID outbreaks have varied but tend to follow introduction of the disease into the United States. For example, the 114th Congress appropriated roughly $5 billion and $2 billion to help control the West Africa Ebola and Zika outbreaks, respectively, but other Congresses did not provide funds to address SARS or yellow fever outbreaks. Due to the unpredictable nature of EID outbreaks, some question whether Congress will continue to emphasize EID that reach U.S. shores or whether the 115th Congress might develop a different approach.
The emergence of yellow fever in areas previously considered not at risk of yellow fever has deepened discussions about mosquito control, human vulnerability to EID, and global capacity to prevent and control large EID outbreaks.
Mosquito control. Brazil is reportedly partnering with a private research company called Oxitec to use genetic modification to control mosquito populations. WHO recommended "carefully planned pilot deployment ... to build evidence for routine programmatic use." Trials have been launched in countries across Latin America and South Asia, as well as in Florida. Despite the WHO endorsement, some health experts are concerned about the efficacy of Oxitec's technology and assert that the release of modified mosquitos might "do more harm than good."
Human vulnerability. Brazil is working to prevent yellow fever from reaching dense, urban areas where most people remain unvaccinated and which are tourist destinations. WHO recommends that yellow fever vaccines be included among routine vaccinations in the 47 countries at risk of yellow fever transmission. Compliance has varied and is hampered by insufficient global production of the vaccine. Health experts warn that incapacity to control a yellow fever outbreak in one country threatens other countries whose populations are not vaccinated against the disease.
Global EID control capacity. During the 2016 central African yellow fever outbreak, WHO employed a "fractional" dosing campaign because of vaccine shortages. Fractional doses protect against the disease for one year while standard doses provide lifetime protection in most cases. Brazil, typically a yellow fever vaccine donor country, is reportedly considering using this strategy and has received 3.5 million doses from WHO.The mass vaccination campaign to stop the central African yellow fever outbreak was the largest such effort in recent history, and trends indicate that other EID might require similar responses. Skeptics question, however, whether sufficient resources exist globally to handle simultaneous outbreaks of a similar magnitude.