People in Rio de Janeiro wait in line to be vaccinated against yellow fever in March. (Ricardo Moraes/Reuters)

U.S. health officials on Friday warned of a new complication in the fight to contain mosquito-borne viruses spreading around the world: The country's supply of yellow fever vaccine is dwindling and will likely be completely gone by this summer — with no way to make more because of a manufacturing problem.

The shortage comes at a troubling time. Multiple outbreaks of yellow fever, which was eradicated in many countries by the 1920s, have popped up around the world in recent years in places such as Angola, the Democratic Republic of Congo and, most recently, Brazil.

The Centers for Disease Control and Prevention's Marty Cetron said the CDC has been collaborating with the Food and Drug Administration and Sanofi Pasteur, which makes the vaccine, to address the shortage by expanding access to a different type of yellow fever vaccine that will be imported from France. That vaccine, Stamaril, is considered investigational and is unlicensed in the United States but is registered in more than 70 other countries and is believed to have a comparable safety and efficacy profile to the one currently in use in the United States.

Stamaril is being made available outside the regular multiyear, multi-layer review process required by the FDA for new vaccines through an “expanded access” provision, which allows for a wider distribution of a drug beyond a limited clinical trial in emergency situations. The provision has more typically been used to grant so-called compassionate use of unapproved drugs to severely ill patients when no alternative is available.

In an interview, Cetron, who oversees the CDC's division of global migration and quarantine, called the plan a “safety net” that will assure a continuous supply of yellow fever vaccine in the United States. However, he acknowledged it would not be without logistical challenges. The main issue for consumers will be that the number of clinics offering the new yellow fever vaccine will be greatly reduced, from about 4,000 to 250, because of the increased complexity of monitoring and data gathering through the expanded access program, which is similar to a clinical trial.

“People who are accustomed to doing things at the last minute should know it may take longer to assure they can get to the right clinic. They should plan ahead,” Cetron said.

He also emphasized that yellow fever is a serious disease — among those who come down with a severe infection, 20 percent to 50 percent die — and that travelers should heed advice to get the vaccine when traveling to an area where the viral disease is present. Estimates of the number of people infected range from 84,000 to 174,000 annually. About 60,000 are believed to die globally each year from the disease, which is transmitted by the same mosquito as Zika.

“This is an important vaccine to get,” he said. “Don't blow it off.”

Issues with the world's supply of yellow fever vaccines have been a source of concern for health officials for years but came into focus during the outbreak in Angola. A UNICEF report released in May 2016 detailed the “constrained” supply and predicted prices would rise.

Before 2000, the demand was about 5 million doses annually. Since 2007, it has been 34 million, and problems at Sanofi Pasteur, one of only four manufacturers, have exacerbated the gap in demand and supply. The yellow bars in the graph below show how steeply the need for the vaccine has increased.


“Yellow Fever Vaccine: Current Supply Outlook,” May 2016. (UNICEF)

Sanofi hasn't released details of the problem but the CDC attributed it to “a manufacturing complication” that resulted in the loss of a large number of doses at the same time it was transitioning from an older to a newer facility. The company said in an email that it anticipated opening its new facility that would resume production of the U.S. version of yellow fever vaccine in mid-2018.

“Sanofi Pasteur recognizes the challenge this supply disruption will cause for customers and for patients in need of yellow fever vaccine,” according to the statement. “We are making every effort to see that yellow fever vaccination continues in the U.S. during this YF-VAX vaccine supply disruption.”

The CDC said that it plans to offer a list of clinic sites for the new vaccine by the end of April at this link. A list of countries that require yellow fever vaccination and information about where the virus is active is available here.