Scientists in the US have warned that the shortage of yellow fever vaccines could spark a global health emergency.
An outbreak of the mosquito-borne viral disease has killed 277 people in Angola since December, according to the UN World Health Organization (WHO).
An article in the Journal of the American Medical Association warns that it could spread to other continents.
The WHO says almost six million people have been vaccinated in Angola, which has a population of 24.3 million.
In April, the WHO said the emergency stockpile of vaccines had ran out.
The virus has already spread to neighbouring Democratic Republic of Congo, Kenya and China.
BBC Africa’s health correspondent Anne Soy says vaccines take around six months to produce, so there is a time lag in responding to a large outbreak like the current one in Angola.
Drug manufacturers globally produce just enough vaccines for routine immunisation, she adds.
In the article, headlined A Yellow Fever Epidemic, A New Global Health Emergency?, two professors from Georgetown University warned that the shortage of vaccine supplies could potentially lead to a health security crisis if it spreads further in Africa, Asia – which has never experienced a yellow fever epidemic – and the Americas.
Daniel Lucey and Lawrence Gostinsay wrote in the journal that the WHO “should urgently convene an emergency committee to mobilise funds, co-ordinate an international response, and spearhead a surge in vaccine production”.
Yellow fever is a virus that can cause bleeding, jaundice and kidney failure, It is spread by mosquitoes, usually the Aedes aegypti mosquito, the same species that spreads the Zika virus.
It is endemic in tropical regions of Africa and South America.
A vaccine can prevent infection but there is no specific drug treatment for people who are infected.