U.S. health officials say the United States will run out of the vaccine for yellow fever as early as next month, and travelers who need a shot might have to wait.
Officials say a manufacturing problem has created a shortage of the only version of the vaccine licensed in the United States.
The vaccine is recommended for travelers to certain parts of South America and Africa, with more than a dozen countries requiring proof of vaccination in order to enter.
The disease was eradicated in the United States more than 100 years ago, and the vaccine is not a part of routine inoculations.
Officials with the Centers for Disease Control and Prevention say they are bringing in another vaccine that is used in other countries to try to lessen the shortage. However, they say it will only be available in about 250 of the 4,000 U.S. clinics that administer the shot.
Health officials are urging travelers to plan ahead, saying it will likely take longer to get the vaccine and people might to need to travel farther to get it.
Yellow fever can cause jaundice, abdominal pain, vomiting, internal bleeding and organ failure. Most people improve after more mild symptoms of fever and chills, however, about 15 percent of infected people become seriously ill.
The virus is spread by the same mosquito that transmits the Zika virus and other tropical diseases. Officials say there has recently been a global shortage of the vaccine.