By EJ Mundell
FRIDAY, April 28, 2017 (HealthDay News) -- As a new outbreak of mosquito-borne yellow fever continues to grow in Brazil, U.S. health officials say they're taking steps to avert any shortage of vaccine travelers might need.
On Friday, the U.S. Centers for Disease Control and Prevention outlined plans to "ensure a continuous yellow fever vaccine supply in the United States," because existing stockpiles are expected to be depleted by mid-2017.
The CDC pointed out that in 2016, Sanofi Pasteur, the maker of the YF-VAX shot against yellow fever, was forced to curb production of the vaccine due to "a manufacturing issue."
"No yellow fever vaccine is expected to be available by mid-2017," the CDC said in a news release. "YF-VAX is the only yellow fever vaccine licensed for use in the United States and is distributed to approximately 4,000 clinic sites."
However, a second yellow fever vaccine, called Stamaril, will be made available at 250 clinics nationwide, the CDC said. Stamaril is manufactured in France by Sanofi Pasteur.
"Because yellow fever is a potentially serious disease, CDC and Sanofi Pasteur collaborated on a plan to distribute limited quantities of Stamaril yellow fever vaccine to prevent people from becoming infected by the virus until production of YF-VAX resumes at a new facility in 2018," the agency explained.
U.S. health officials have recently sounded the alarm over yellow fever.
In an essay published April 13 in the New England Journal of Medicine, Dr. Anthony Fauci, director of the U.S. National Institute of Allergy and Infectious Diseases, and colleague Dr. Catharine Paules said that a large outbreak of yellow fever in Brazil must be closely monitored.
Yellow fever has a relatively high death rate and "is the most severe [insect-transmitted] virus ever to circulate in the Americas," Fauci and Paules wrote.
"Although it is highly unlikely that we will see yellow fever outbreaks in the continental United States . . . it is possible that travel-related cases of yellow fever could occur, with brief periods of local transmission in warmer regions such as the Gulf Coast states, where A. aegyptimosquitoes are prevalent," the team added.
According to the infectious disease experts, yellow fever has the potential to be the fifth mosquito-borne infection to appear in the continental United States since the 1990s, following dengue, West Nile, chikungunya and the Zika virus.
Yellow fever is perhaps the most dangerous of those five, however. In one outbreak that began in the Congo in December 2015, there were 137 deaths among 961 confirmed cases, the report noted.
And in the current Brazilian outbreak, there have so far been hundreds of cases and dozens of confirmed deaths, according to health authorities.
More ominous in the Brazilian outbreak is the fact that the illness appears to be moving from its typical rural setting towards the cities.
"The outbreak is affecting areas in close proximity to major urban centers [in Brazil] where yellow fever vaccine is not routinely administered," Fauci and Paules warned.
The authors stressed that there's no evidence yet that mosquitoes are transmitting yellow fever between infected people. However, the advent of outbreaks near urban centers "raises concern that, for the first time in decades, urban transmission of yellow fever will occur in Brazil," they explained.
The disease is not a complete stranger to the United States, although scientists say the last major outbreak lies far back in history.
"The Philadelphia yellow fever epidemic of 1793, for example, killed approximately 10 percent of the city's population," Fauci and Paules noted.
Luckily for Americans today, the yellow fever vaccine -- first developed in 1937 -- is effective in preventing illness. The current vaccine is thought to be 99-percent effective over a lifetime.
For those already infected, it's crucial that symptoms are spotted early.
However, "early recognition may be difficult in countries such as the United States, where most physicians have never seen a case of yellow fever," the authors pointed out. Early symptoms include a fever that can mimic flu, followed by a period of remission, and then a stage called "intoxication" -- high fever, liver dysfunction and jaundice, and even kidney failure, heart and nervous system dysfunction, and shock.
No such cases have emerged in the United States, but international travel means unvaccinated people might bring the illness back home after visiting an endemic area.
The yellow fever outbreak comes as the Zika virus continues to affect countries throughout the Americas. Both viruses are spread by the same mosquito species.
To prevent the Brazil outbreak from spreading, "early identification of cases and rapid implementation of public health management and prevention strategies, such as mosquito control and appropriate vaccination, are critical," Fauci and Paules concluded.