The global stockpile of the yellow fever vaccine may not be sufficient if simultaneous outbreaks hit the densely populated areas not covered by emergency responses, the United Nations health agency has warned, noting that by mid-June 2016, almost 18 million doses have been distributed in Angola, Democratic Republic of the Congo (DRC), and Uganda this year.In particular, the Angola outbreak has depleted six million doses twice this year already, a level never seen before. In the past, no more than four million doses have been used to control an outbreak in one country.According to the World Health Organization (WHO), which raised the concern today, the world’s four major vaccine manufacturers have been working around the clock to replenish the stockpile, bringing the global stockpile to 6.2 million doses in early June.Urban yellow fever can spread rapidly in densely populated cities, causing thousands of deaths and very serious humanitarian consequences. Vaccination is the most important measure for preventing the disease. But production takes a long time – around 12 months – and it is difficult to forecast in advance the quantities that will be needed each year to respond to outbreaks.In 1997, WHO, in partnership with the UN Children’s Fund (UNICEF), Médecins sans Frontières (MSF) and the International Federation of the Red Cross and Red Crescent Societies (IFRC), created the International Coordinating Group (ICG) to manage emergency vaccine stockpiles for future outbreaks and coordinate the distribution of vaccines to the affected areas.Yellow fever was first confirmed on 19 January 2016 in Angola. Nine days later, the Angolan Ministry of Health requested 1.8 million doses from the global stockpile of emergency vaccine supplies, which was approved the same day.Since then, the country has made several additional requests for vaccines from the emergency stockpile and by 18 May had received 11.7 million doses in total. Ongoing vaccination campaigns due to the further spread of the disease are putting continuous demands on the stockpile.In addition, outbreaks in Uganda and the DRC have stretched the global supply with demands for more than 700,000 and 2.2 million doses respectively.Yellow fever is an acute viral haemorrhagic disease transmitted by infected mosquitoes. The ‘yellow’ in the name refers to the jaundice that affects some patients. Symptoms of yellow fever include fever, headache, jaundice, muscle pain, nausea, vomiting and fatigue.