Editor’s note: This story was updated Aug. 16, 2016, with updated case numbers and the WHO using lower doses of vaccine in order to reach more people.
WebMD spoke with specialists about the illness and the likelihood of it arriving on our shores -- again.
What is yellow fever?
Most people with the disease will have mild symptoms and may not know they're sick, says infectious disease specialist Sunil K. Sood, MD, chair of pediatrics at Northwell Health’s Southside Hospital.
But about 15% of people with yellow fever will develop serious, life-threatening complications.
“It’s potentially a very serious illness because the liver is involved,” Sood says. “It can be fatal.”
Those people get a high fever, bleeding, shock, and organ failure. Their skin and the whites of the eyes become jaundiced, the yellowing that gives the disease its name. The CDC estimates that 20% to 50% of those who get this stage of the illness will die.
How is yellow fever diagnosed and treated?
Travelers who come home from affected countries should get medical help if they have a fever or get one shortly after returning, Sood says. “Whenever a returning traveler has a fever, a whole list of diseases should be considered based on where they went,” he says. “If they were in the part of Africa where there’s yellow fever, that disease should be on the list.”
“If their symptoms are mild, they can be observed as outpatients,” Sood says. “If it’s serious, they would be hospitalized.”
While there’s no cure for disease, it usually passes within a few days. If it becomes serious, doctors will give you what Sood calls supportive care.
“If there’s fever, we treat the fever. If there’s bleeding, we treat the bleeding. If the liver does happen to be severely affected, there are treatments, generally involving IV fluids, to help with that.”
What is happening in Africa?
The most recent outbreak began in early December 2015 in Luanda, the capital of Angola, says the CDC’s Martin Cetron, MD. The first cases were officially diagnosed in January 2016. As of Aug. 4, there have been more than 3,800 suspected cases, with more than 800 confirmed. Nearly 370 people have died, including nearly 120 confirmed cases, according to the WHO.
Most of the cases have happened in Luanda, but the disease also has been identified in several other Angolan provinces. And travelers from Angola have carried the disease to the Democratic Republic of the Congo (DRC), Kenya, and China.
The cases in the DRC are also considered an outbreak, the WHO says. As of Aug. 8, more than 2,200 suspected cases have been reported and nearly 75 have been confirmed. Most of them were imported from Angola, according to the WHO. Sixteen people with confirmed cases have died. The number of reported deaths was not available, but the WHO previously said that number was at least 95.
Cases have also been seen in Uganda, but they have not been linked to the Angola outbreak. That outbreak is under control, according to the WHO. Other countries seeing outbreaks or cases not linked to Angola are Brazil, Chad, Colombia, Ghana, and Peru.
“It’s a dynamic situation,” says Cetron, director of the CDC’s Division of Global Migration and Quarantine.
And a difficult one. The mosquito that spreads the disease in urban areas, Aedes aegypti, is hard to control. Cetron calls it the “cockroach of mosquitoes.” It likes to bite humans, prefers the indoors, and feeds in the daytime. (Aedes mosquitoes also spread the Zika virus.)
Once the virus gets into an urban area and into Aedes aegypti mosquitoes, you start to get major epidemics, Cetron says. “It’s the density of the housing, it’s human behavior, it’s the biting patterns of the mosquitoes, it’s the climate. There are so many factors that go into it.”
Is there a vaccine?
Yes, and Cetron says it’s an excellent one. Problems are rare, and it gives most people lifelong protection, he says.
The WHO, which stockpiles yellow fever vaccine, has launched a massive vaccine campaign to control the spread of the virus. Cetron says their efforts resulted in nearly 90% coverage in the target area of Luanda. That may not be enough, though.
“Unfortunately, cases have now been reported in other provinces, where vaccination has not yet begun,” he says. “There’s still epidemic potential in these other provinces, and the challenge we’re now running into is a shortage in the emergency stockpile of vaccine.”
The vaccination campaign previously was launched along the border of Angola and the DRC as well as the city of Kinshasa in the DRC. As of Aug. 16, more than 13 million people in Angola and 3 million in the DRC have been vaccinated, the WHO says.
However, the agency in mid-August stepped up vaccination efforts to reach even more. Kinshasa has more than 10 million people, with only 2 million already vaccinated, according to the WHO, and “there is a potential risk that the deadly outbreak could spread to other urban areas.”
The WHO says the outbreaks have “placed great demand on the global supply.” The global stockpile of 6 million vaccines for emergency response, usually enough for a year, has already been replenished twice this year, the agency says.
Facing a limited vaccine supply and a minimum 6-month manufacturing process, the mid-August vaccination campaign is using one-fifth of the standard vaccine dose per person in what the WHO says is a “short-term emergency measure to reach as many people as possible.” This approach was recommended by a WHO expert panel. While the lower dose will not permit people to travel internationally, it will protect them from yellow fever during the current outbreak and help curb the spread of the disease.
Who needs to get the vaccine?
If you don’t live in the affected areas, you don’t need a vaccine. But all travelers over the age of 9 months should be vaccinated before traveling to affected regions.
Be aware of the risks if you're going to areas with cases of yellow fever, says infectious diseases expert James Le Duc, PhD, director of the Galveston National Laboratory. “Get vaccinated if you plan to travel to tropical Africa, as this has the potential to spread.”
Travelers to Angola are not allowed to enter the country without proof of vaccination.
Should Americans be concerned about yellow fever in the United States?
There have been yellow fever epidemics in the U.S. throughout its history. The worst happened in 1878, when an outbreak in New Orleans spread throughout the Mississippi Valley region, sickening more than 120,000 and killing at least 13,000.
But it’s unlikely we’ll see large outbreaks in the U.S. today, Le Duc says. Instead, we may see small clusters and isolated cases. The size of any outbreak likely will depend in part upon how well mosquitoes are controlled in a given area. That varies from place to place and is often the responsibility of county governments.
“Each county has a different approach, and there’s a wide range of how well vectors [mosquitoes] are controlled in general,” Le Duc says. “Areas that lack a robust vector control program and have a large population of Aedes aegypti mosquitoes may see some transmission of the disease.”
Those mosquitoes are found throughout the South and in parts of the East Coast and Midwest.
Le Duc says the WHO and the CDC are taking the Angola yellow fever outbreak seriously and are acting appropriately.
“This has the potential of being a very serious disease, and the aggressive response that’s being taken is important,” he says. “Right now, it’s under the radar for most of the world, but it could rear up like Ebola did and be a real mess.”