With the spread of the yellow fever epidemic across African nations, health officials are working to stretch the limited supply of vaccines.

The World Health Organization (WHO) has not yet declared the outbreak a public health emergency, but is concerned about the possible shortage of vaccines to fight the disease.

According to a statement by WHO, the global stockpile of 6 million vaccines for emergencies has already been replenished twice this year, while the amount should have been enough to last a whole year.

As a response, the agency proposed to use one-fifth of the regular dosage for the yellow fever vaccine during emergency shortages.

"Right now we have enough vaccines in the global stockpile to cope with the ongoing outbreaks if there are no further extensions," Jon Abramson, chair of the WHO Strategic Advisory Group of Experts (SAGE), announced last week.

"However, given the wide spread of the disease in Angola and the potential for it to get out of control in the city of Kinshasa, in the Democratic Republic of the Congo, WHO and partners are seriously considering the use of this dose-sparing strategy to prevent transmission through large-scale vaccination campaigns," Abramson added.

The yellow fever outbreak was first identified in Angola in December 2015. The country has reported 3,100 cases to date. 

Health officials in the Democratic Republic of Congo (DRC) on Monday declared an epidemic of yellow fever in three regions, including the capital Kinshasa. Officials confirmed 67 cases of the disease and 1,000 more suspected cases being monitored, Reuters reported.

Kenya and China have also reported cases of yellow fever brought to the country by travelers. Other countries, including Brazil, Chad, Colombia, Ethiopia, Ghana, Peru and Uganda have also reported outbreaks of yellow fever, which appear to be unrelated to the outbreak that started in Angola.

Yellow fever is caused by both Aedes and Haemogogus mosquitoes. People infected with yellow fever may show mild symptoms or no symptoms at all. Symptoms include fever, chills, aching, nausea and fatigue. Some cases may lead to severe diseases such as high fever, bleeding, jaundice or even shock and organ failure.