More than 400 people have died from yellow fever in Africa, the World Health Organization said Thursday.
The WHO and other groups are trying to help Angola and the Democratic Republic of the Congo fight worsening outbreaks of the deadly, mosquito-borne virus.
More than 3,000 cases have been reported in Angola, the epicenter of the outbreaks, the WHO said. "The total number of reported deaths [there] is 345," the organization added in an update.
"Mass vaccination campaigns first began in Luanda and have now expanded to cover most of the other affected parts of the country, recently the campaigns have focused on border areas. Despite extensive vaccination efforts, circulation of the virus persists."
And more than 1,000 suspected cases are reported in the Democratic Republic of the Congo, with 71 deaths. A few cases have also been reported in Kenya and China — carried by travelers. Uganda has had 30 cases and seven deaths.
"Seven countries (Brazil, Chad, Colombia, Ethiopia, Ghana, Peru and Uganda) are currently reporting yellow fever outbreaks or sporadic cases not linked to the Angolan outbreak," the WHO added.
Yellow fever is carried by mosquitoes. It's a relative of dengue, Zika and chikungunya but is far deadlier. It's also the only virus in the family that has a good vaccine to prevent it.
But supplies haven't always been distributed as and where needed.
"The outbreaks of yellow fever in Angola, Democratic Republic of the Congo and Uganda have placed great demand on the global supply of yellow fever vaccines," the WHO said.
"The global stockpile of 6 million vaccines for emergency response (normally enough for a year) has already been replenished twice this year."
The WHO says it will be difficult to control the spread of the virus.
"As the borders are porous with substantial cross border social and economic activities, further transmission cannot be excluded," it said.
Yellow fever can be mild. Symptoms include fever, headache, jaundice, muscle pain, nausea, vomiting and fatigue. It's the jaundice that gives yellow fever its name.
"A small proportion of patients who contract the virus develop severe symptoms and approximately half of those die within seven to 10 days," the WHO said. Although it's unrelated to Ebola, yellow fever can cause similar bleeding symptoms. Like so many other infections, it can look like malaria, hepatitis, other viruses or even poisoning.
"Large epidemics of yellow fever occur when infected people introduce the virus into heavily populated areas with high mosquito density and where most people have little or no immunity, due to lack of vaccination. In these conditions, infected mosquitoes transmit the virus from person to person," the WHO said.