Francesca Tomasi received her B.A. from the University of Chicago and currently does microbiology research.
In July, 1793, Philadelphia was the capital of the United States. It was an urban hub packed with colonists and free ex-slaves alike. The city bustled with the energy of a new nation as people came and left, conducting business and politics, building new lives for themselves.
In July, 1793, an outbreak of yellow fever ignited and tore through the city. In a matter of months, the infectious disease killed ten percent of Philadelphia’s population of 50,000 people, prompting 17,000 more residents to flee the city in a justifiably terrified frenzy. The outbreak raged through the summer and fall. Thomas Jefferson wrote many letters to friends and partners during the epidemic, describing both the outbreak and the panic that were plaguing the city. Here’s an excerpt from a letter to James Madison:
“A malignant fever has been generated in the filth of Water street which gives great alarm. About 70 people had died of it two days ago, & as many more were ill of it. It has now got into most parts of the city & is considerably infectious. At first 3 out of 4 died. Now about 1 out of 3. It comes on with a pain in the head, sick stomach, then a little chill, fever, black vomiting & stools, & death from the 2nd to the 8th day. Every body, who can, is flying from the city, and the panic of the country people is likely to add famine to disease. Tho becoming less mortal, it is still spreading, and the heat of the weather is very unpropitious. I have withdrawn my daughter from the city, but am obliged to go to it every day myself.”
Infection with the yellow fever virus starts with fever and muscle pain. Next come its first characteristic symptom, the namesake of the virus: victims develop jaundice as a result of liver and kidney failure. The most severe cases also developed a second characteristic, black vomit. In fact, the Spanish name for yellow fever is vomito negro, named after this symptom. This bloody vomit is a result of internal bleeding in the digestive tract. Delirium hits and as many as 89% of victims die.
The yellow fever outbreak came to a pretty abrupt end in November. There were many theories about its origin. One physician in Philadelphia named Benjamin Rush (you might recognize his name from the Declaration of Independence) thought the outbreak arose from contaminated, rotting coffee beans left on the city docks. He treated patients by bleeding them profusely and infusing them with mercury. Rush also believed that African Americans were immune to the disease, so he enlisted black volunteers as nurses. Of course, this theory turned out to be false, and African Americans soon became seriously ill and died at the same rates as white people.
Nothing was known about the yellow fever virus or how it spread until the end of the 19th century. Now, however, we know enough to have a vaccine that prevents the disease in much of the world. We know that the Philadelphia outbreak in 1793 was carried over from the Caribbean by refugees of an outbreak taking place there. We also know that a cold front in November ended the epidemic because the emerging winter frost killed off the city’s mosquito population.
Yellow fever is related to several viruses you may have heard of, including West Nile and Japanese encephalitis viruses. It is transmitted by infected Aedes and Haemagogus mosquitoes, which acquire the virus by feeding on infected humans and other primates. Today, yellow fever is rarely a cause of illness in the United States unlike in the 17th and 18th centuries. Instead, it is predominantly found in tropical and subtropical regions of South America and Africa.
There is a highly effective vaccine against yellow fever, which is why major outbreaks of the disease are so rare nowadays. The vaccine is recommended for anybody older than 9 months who lives in or is traveling to at-risk regions. In fact, many at-risk and neighboring nations require proof of vaccination for individuals traveling there. The yellow fever vaccine confers lifelong immunity in most people, another feature that contributes to its great effectiveness. There is currently no specific antiviral drug or immune therapy to treat someone who has been infected with the virus, which is why prevention is key.
Yellow fever had a happy ending in the United States and many other parts of the world. The vaccine has done an incredible job quelling this disease. However, a common theme in infectious diseases is the persistence of otherwise eradicated infections in poor regions lacking adequate public health infrastructure. This, coupled with a global shortage of the yellow fever vaccine, is triggering what some are calling a new global health emergency.
Zika virus has been getting a lot of attention lately because of its newfound neurological effects on developing fetuses and the fact that it is spreading like wildfire in parts of North and South America. However, an epidemic on one side of the world shouldn’t turn the world blind to a different epidemic raging somewhere else. Currently, the worst yellow fever epidemic in Angola is infiltrating the country (including the nation’s capital, Luanda). The outbreak began in December 2015, roughly the same time that Zika started gaining international attention. As of April 26, 2016, the disease has sickened over 2,020 people and killed at least 260. Infected travelers have also brought yellow fever to China, the Democratic Republic of Congo, Kenya, and Angola’s bordering nations Namibia and Zambia.
An article published by two members of faculty at Georgetown University calls for international attention to the outbreak. Notwithstanding the fact that over 7 million Angolans have been vaccinated against yellow fever, the ongoing global vaccine shortage could cause the epidemic in Angola to escalate as more people are infected and travel to other parts of the world where Aedes mosquitoes live (including the rest of Africa, Asia, and the Americas). The authors of the article call on the WHO to “convene an emergency committee to mobilize funds, coordinate an international response, and spearhead a surge in vaccine production.” They draw on “prior delays” by the WHO in assembling for these purposes such as during the 2014 Ebola epidemic, underscoring the hazard of not immediately and proactively addressing the unfolding yellow fever outbreak.
Earlier this month, the Democratic Republic of Congo announced a vaccination program against yellow fever aimed at immunizing 2 million individuals in Kinshasa and Kongo Central as a preventive strategy against the Angola outbreak: health officials in the DRC suspect local transmission of the virus and are working to quell a serious outbreak. This campaign, piled onto vaccination campaigns in the hard-hit nation of Angola, will really stretch the world’s yellow fever vaccine supplies thin, possibly even completely depleting them. For these reasons, people are calling on the WHO’s Emergency Use Assessment and Listing procedures, which were first used during the Ebola epidemic. These guidelines were established to expedite the availability of diagnostics, vaccines, and/or treatments in public health emergency situations. Such an intervention is highly called upon in the case of the ongoing yellow fever outbreak to prevent a possible pandemic. In this case, the WHO could authorize a reduced vaccine dose in order to reach more people while new vaccine stocks are produced. Of course, we don’t know the quality and duration of protection of a diluted vaccine. However, some protection is better than none, and such stewardship of existing vaccine stockpiles is a regulatory affair that requires official convening of an emergency committee. In the meantime, vaccine manufacturers should look into methods for vaccine development that do not require multi-stage egg incubation. Furthermore, mosquito control programs in the Americas currently being implemented to fight Zika should also make their way to Angola and neighboring regions.
Here’s what the WHO has to say about the outbreak in Angola, posted on April 13, 2016:
"The evolution of the situation in Angola is concerning and needs to be closely monitored. The reports of imported cases of YF in China, DRC and Kenya demonstrate that this outbreak constitutes a potential threat for the entire world. There is a risk for the further spread of the disease in view of the large international communities residing in Angola and the frequent travel activities with neighbouring and overseas countries. Furthermore, all countries where the mosquito vector (Aedes species) is present are at risk, notably those endemic for or previously affected by outbreaks of Dengue, Chikungunya or Zika virus and other arboviruses. Therefore, there is an urgent need to strengthen the quality of the response in Angola and to enhance preparedness activities in neighbouring countries and in countries that have diaspora communities in Angola. WHO continues to monitor the epidemiological situation and conduct risk assessment based on the latest available information."
Yellow fever now kills 80,000 Africans every year. As The Economist puts it bluntly yet accurately, “that is a scandal…because it can be prevented by a single inoculation.” This “scandal” will only explode if the current outbreak goes pandemic. Yellow fever vaccine production is controlled by the French drug company Sanofi Pasteur as well as institutes in Brazil, Senegal, and Russia. The world’s emergency yellow fever vaccine stockpile houses approximately 11 million doses. The ongoing outbreak, however, has the potential to go global if not controlled. If this turns out to be the case, 11 million doses will not even scratch the surface: should the virus reach naïve Asia (naïve meaning the virus has never before spread there), the number of people at risk would leap from tens of millions to over one hundred million.