Global rise of yellow fever necessitates vaccine increase

Dear Doctor: I read that hospitals in the United States might run out of yellow fever vaccine soon. I'm a natural worrier, but I can't help wondering if yellow fever really is an issue in this country.

Dear Reader: It has been more than a century since the last major outbreak of yellow fever in the U.S. But with several recent new outbreaks throughout the world, including one in Brazil, the supply of yellow fever vaccine is running low at a difficult time.

To understand why the resurgence of yellow fever has health professionals concerned, let's take a closer look at the disease.

Yellow fever is a flulike illness spread by certain species of mosquitoes that are infected with the virus. It affects both monkeys and humans, and is carried between the species by the infected insects.

Not everyone who contracts the virus develops symptoms, which can range from mild to severe. In less-serious cases, patients experience fever, chills, headache, muscle aches, nausea and vomiting. Jaundice, which causes the skin and whites of the eyes to appear yellow and can also be a symptom, is how the disease got its name.

In the small proportion of people who go on to develop a severe form of yellow fever — about 15 percent of those who are infected — the disease can cause uncontrolled bleeding, and result in heart, kidney and liver problems. According to the World Health Organization, half of the severe cases of yellow fever are fatal.

The disease, which is believed to have originated in Africa, became an international problem in the 1600s, when shipping began to go global. The infected mosquitoes were transported throughout the world, and yellow fever epidemics began to occur.

During the Spanish-American War, five times as many American soldiers died of yellow fever as did in battle. This led to the formation of a commission that proved what had been suspected since the mid-1800s — that the disease is spread by mosquitoes. Subsequent sanitation programs, followed by the development of a pair of vaccines in the 1930s, led to the near-eradication of the disease in many areas. The last outbreak in the U.S. occurred in New Orleans in 1905.

Now, because of an increase in disease among monkeys, flagging vaccination programs in some countries, and the mosquito-friendly environment caused by a warming planet, infected mosquitoes are on the move again. This has caused a spike in demand for the vaccine. Prior to 2000, about 5 million doses per year were adequate. By 2007, demand rose to 34 million doses of the vaccine.

American health officials, who say the outbreak in Brazil is uncomfortably close to home, are working to expand the supply of vaccine. Sanofi Pasteur, the main vaccine producer, announced plans to open a new manufacturing facility in the U.S. next year.

In the meantime, federal health agencies are working to make available an alternate vaccine that is imported from France. Clinic sites with this vaccine are listed here: wwwnc.cdc.gov/ travel/yellow-fever-vaccination-clinics/search.