Update on Investigational Yellow Fever Vaccine for Travelers

Updated: 8/15/2017 at 11:00 AM EST

A yellow fever outbreak in Brazil that began in December of 2016 has continued to grow in this and several other South American countries. In addition, unavoidable disruptions in manufacturing have led to shortages of the conventional vaccine for the virus for Americans looking to travel to Brazil and other affected areas. As a result, an alternative vaccine made available in other countries has received approval in the United States, and can be found in vaccination clinics around the country.

Yellow fever is a mosquito-borne virus which has caused outbreaks in North America centuries ago and is now mostly isolated to tropical and subtropical parts of Africa and South America. Aedes and Haemagogus mosquitoes transmit the virus from infected humans and non-human primates. Most people who become infected with yellow fever do not present with symptoms or only exhibit mild illness. When symptoms do occur, they typically develop within 3 to 6 days of infection and can include fever, severe headache, chills, back and body aches, and nausea. While symptoms clear in most infected individuals, infection can become more severe in about 15% of cases after a brief remission period. This can result in high fever, jaundice, bleeding, and even organ failure. Up to half of those who develop severe yellow fever symptoms die.

In Brazil, a large outbreak of yellow fever has continued to grow. According to a recent situation summary from the Pan American Health Organization (PAHO), Brazil has reported 3192 suspected cases since December 2016. Of those, health officials have confirmed 758 cases, discarded 1812, and is continuing to investigate 622 cases. Brazil’s Ministry of Health has reported 426 deaths linked to the outbreak, which equates to a 34% fatality rate among confirmed cases. In addition, the country has reported 3660 deaths in non-human primates since the start of the outbreak, with yellow fever confirmed to be the cause of 565 deaths, and 1467 deaths still under investigation.

The Centers for Disease Control and Prevention (CDC) recently stated that YF-VAX maker Sanofi Pasteur announced that the vaccine will be unavailable until mid-2018. To this end, Sanofi advised Contagion® that, “Some of the yellow fever vaccine doses used in response to the outbreak in Brazil were procured through the ICG (the International Coordinating Group) to which Sanofi Pasteur contributes STAMARIL doses as part of a global stockpile for managing situations such as we are seeing in Brazil and saw in Angola in 2016.”

Although the outbreak has largely remained in low population areas of Brazil, the recent PAHO update notes that health officials have directed the use of the investigational yellow fever vaccine, STAMARIL, to prevent these outbreaks from spreading into more populated, urban areas. In recent months 24.5 million doses of STAMARIL have gone to a selective vaccination strategy in more than 1,000 Brazilian municipalities. As a result, 285 municipalities in the country have achieved more than 95% vaccination coverage, while 375 municipalities have achieved between 74% and 94.9% coverage.

STAMARIL is already available in more than 70 countries. In the United States, the vaccine has been FDA-approved through an Expanded Access Investigational New Drug Application, meaning that it is still considered investigational. Due to this limitation, “Sanofi Pasteur can support only a limited number of sites,” including several US vaccination clinics; however, the pharmaceutical company is working with the CDC to expand distribution of and access to the vaccine. According to Sanofi, “Should additional vaccine requests be communicated to Sanofi, we will continue to work with international organizations and healthcare providers/customers on best options to offer STAMARIL to people who need to be vaccinated, be they populations living in endemic or affected areas, or international travelers.”

The CDC recommends one dose of the yellow fever vaccine for those ages 9 months or older who are traveling to areas experiencing outbreaks of the virus, or to countries in sub-Saharan Africa and tropical South America where the virus is endemic and intermittently epidemic. Those travelling to Brazil or other countries with active yellow fever outbreaks should receive the vaccine at least 10 days before entering an affected area to ensure they have receive protective immunity. The World Health Organization Advisory Group of Experts on Immunization notes that one dose of the vaccine offers lifelong protection from the yellow fever virus.

Editor’s Note: A previous version of this article implied that the yellow fever outbreak in Brazil and other South American countries led to a shortage of the vaccine. This is incorrect. The shortage is due to unavoidable disruptions in manufacturing, and not related to an outbreak.