In the wake of news of 10 travelers being infected with yellow fever, 4 of whom have died, the Centers for Disease Control and Prevention (CDC) are urging anyone considering travel to yellow fever endemic regions of Brazil to be vaccinated prior to travel.
In January 2018, the World Health Organization (WHO) announced that anyone planning to visit São Paulo, Brazil, should consider receiving the yellow fever vaccine before their trip. Additional areas included in the recommendations were Espírito Santo, Rio de Janeiro states, and certain cities in Bahia state. That message of consideration has turned into a severe warning as 10 travel-related cases of yellow fever have been reported and 4 of those travelers have died. None of the travelers had been vaccinated against the virus.
Yellow fever, which is endemic to South American and sub-Saharan Africa, typically causes an asymptomatic infection; however, among those individuals who develop severe illness (15%), the case fatality rate is 20% to 60%, according to the Centers for Disease Control and Prevention (CDC).
The number of infected individuals living in Brazil was 723 as of February 28, while the death toll has hit 237. WHO reports that this increase “is likely due to yellow fever virus circulating in areas of the country that have the highest concentrated population and in areas in which yellow fever vaccination was not previously recommended.” Those cases were reported in the following states:
Eight of the travelers to Brazil who were infected with yellow fever acquired the virus in “Ilha Grande, a forested island off the Rio de Janeiro coast, where 1 human and 1 nonhuman primate yellow fever case were reported in early February 2018,” according to a recent Morbidity and Mortality Weekly Report (MMWR) from the CDC. Four of the 8 individuals who acquired the virus on Ilha Grande died.
The CDC hosted a teleconference today (March 16, 2018) to discuss the outbreak. Martin Cetron, MD, Director for the Division of Global Migration and Quarantine (DGMQ) remarked that the “intensity of transmission is unprecedented among travelers,” and that it is highly unusual to see this cluster of cases.
Because the approximate number of individuals who travel from the United States to Brazil is about 2.2 million each year, media representatives on the call asked about the risk of yellow fever being brought back into the United States (as has been seen with Zika). Lyle R. Petersen, MD, MPH, Director, Division of Vector-Borne Diseases, National Center for Emerging and Zoonotic Infectious Diseases (NCEZID) explained that the risk is minimal. “The yellow fever virus is spread by 2 mosquitoes: forest-dwelling mosquitoes and Aedes aegypti mosquitoes,” shared Dr. Petersen. “What’s happening in Ila Grande is that people are going into the forest and being infected. Aedes aegypti are urban mosquitoes, and while the virus is not being spread by those mosquitoes right now in Brazil, that’s the fear.” Although the United States does have Aedes aegypti, it does not have forest-dwelling mosquitoes, and so while there is potential for yellow fever to be brought back and spread in the United States; if it did, the spread would be minimal, according to Dr. Petersen.
Although Antonio Carlos Nardi, MD, Brazil’s Deputy Health Minister previously stated Brazil is not in the midst of a yellow fever outbreak, and instead only seeing an increase in cases, the country ramped up their vaccination efforts, vaccinating 5,525,080 individuals as of February 28, 2018, according to the WHO. A total of 5,031,089 of these individuals were provided a half-dose of the vaccine, which is capable of providing immunity for 8 years. (A full dose of the vaccine is able to confer lifetime immunity.) Despite these high numbers, there is still a long way to go to hit the goal of vaccinating 23,812,288 individuals.
The CDC recommends that all eligible individuals 9 months of age and older who are traveling to Brazil—including the states of São Paulo and Rio de Janeiro (especially Ilha Grande)—should receive the yellow fever vaccine. Although YF-VAX, the US Food and Drug Administration (FDA)-approved yellow fever vaccine is unavailable in the United States (because of manufacturing issues), Stamaril, an alternative yellow fever vaccine, is available at a limited number of US yellow fever vaccination clinics.
Travelers to Brazil are strongly urged to be vaccinated at least 10 days prior to travel, even if they are traveling to the affected areas on business and have no plans to visit forested areas. “The risk is markedly increased,” said Dr. Cetron. “Monkeys are dying off on the outskirts of São Paulo city and in São Paulo zoo and it’s not hard to walk to a forested area with risk of transmission. Just don’t chance it. If you’re going there, get vaccinated.”
All unvaccinated travelers should not travel to areas where vaccination is recommended. According to the CDC, “clinicians assessing return[ing] travelers should be aware of yellow fever signs and symptoms and maintain vigilance regarding the possibility of yellow fever exposure in travelers returning from Brazil or other areas with ongoing transmission of yellow fever.”