Health officials have reported the world’s worst yellow fever outbreak in decades. The outbreak originated in an Angolan slum because of a migrant victim’s false vaccine documents. Medical experts failed to detect the disease early on because the victims were Eritrean migrants whose false documents led the doctors astray in terms of trying to figure out the disease. The disease escalated quickly and so far has killed 325 people in Angola and has spread as far as China, which has raised concern for the world’s vaccine supply running out. The spread of the virus could have been limited if its origination were identified quickly in Luanda.

Yellow fever is transmitted by the same mosquito that carries dengue and Zika viruses, although it is more lethal, causing 75% deaths in severe cases requiring admission to hospitals and is associated with the yellowish jaundiced appearance of its victims. Since the outbreak was identified in January, 10.5 million Angolans, which is approximately 40 percent of the population, have been vaccinated and the World Health Organization (WHO) plans to cover the rest of the war-ridden country’s population by the end of 2016. But with a reported case of the disease spreading via a mosquito from one person to another in Kinshasa, a city of over 12 million in the neighboring country of Democratic Republic of Congo, there are apprehensions about shortage of global vaccine supplies.

Hernando Agudelo, a Luanda WHO representative said he and government officials thought they were dealing with a mystery disease when unexplained deaths first surfaced in Km 30, part of the capital’s immense Viana district, in December. Agudelo said that the first people they found dying had vaccination documents and could not comprehend what disease caused these symptoms.

With the recent carnage of the West African Ebola virus, Angola and WHO officials were extra cautious and were mindful of leaving no stone unturned in finding the causes of the outbreak. They quickly narrowed it down to a restaurant in Km 30, home to the biggest informal market in the city of 7 million, in the municipality of Viana as the link between the victims. Agudelo said they started to investigate the vicinities of the source of the virus and found the link that they were from Eritrea and had passed through the same restaurant.

Most people flee Eritrea to Europe due to the evil dictatorship ruling over the country. Some also head towards Angola where entry is granted only on providing valid vaccine documents. Due to the catastrophic conditions at home under President Isaias Afwerki, who has been in charge of the helm since 1991, many Eritreans fake documents to gain entry.

After the passing of the restaurant owner, test samples were sent to South Africa’s National Institute of Communicable Diseases, where technicians who had been told about the vaccination papers only ran a yellow fever test out of a hunch, according to Agudelo. WHO reported yellow fever being tested on January 19, 2016. But by that time the viral outbreak had long since spread from Viana, and by February suspected cases were recorded in more than half of Angola’s 18 provinces. In April, victims who contracted it in Angola were dying in Congo.

The outbreak drastically affected Angola’s economy, being the biggest oil producer in Africa. The collapse in oil revenues has greatly hampered the national budget since 70% of it comes from oil production.

Routine yellow fever vaccination only started in the late ’80s and only covers 70% of the population. Nearly all of Luanda’s population has now been vaccinated but the mass vaccination campaign has come with a cost of depleting the world’s emergency vaccine stockpile and the stock cannot be restocked immediately.

Manufacturers, including the Institut Pasteur, government factories in Brazil and Russia, and French drugmaker Sanofi, use a slow-paced production technique that involves sterile chicken eggs. Should the disease take hold in Kinshasa, one of Africa’s biggest cities, health officials may have little to stretch out the world stockpile of 6 million shots by limiting the dosage to one-fifth doses. In Luanda, health officials are regretting the missed early opportunities and the immense expenses that has now entailed.

“If we had contained this at the Luanda level, we would not have had to spend the money that we’re spending now,” said Francisco Sondane, a medical doctor running UNICEF’s operations in Angola. According to reports generated by WHO, nearly 3,000 people died of malaria in the first three months of this year, compared to 8,000 in the whole of 2015, and there is a possibility of outbreaks of diseases such as cholera, typhoid or plague in the near future due to the country’s poor economic situation.