The Angola military administers yellow fever vaccine at the Quilometro 30 market in Luanda in February.

The Angola military administers yellow fever vaccine at the Quilometro 30 market in Luanda in February.

© JOOST DE RAEYMAEKER/epa/Corbis

Yellow fever threat is ‘serious’ but not an ‘emergency,’ WHO says

After weeks of growing alarm about the ongoing urban outbreaks of yellow fever in Angola and the Democratic Republic of the Congo, an emergency committee convened by the World Health Organization (WHO) lowered the pitch a little today. It called the outbreak “a serious public health event,” but because the international spread of the disease has slowed and vaccine supplies are recovering, the committee stopped short of declaring it a “public health emergency of international concern” (PHEIC). That label would have given any recommendations from WHO greater power. (The organization has declared a PHEIC four times: for H1N1 influenza, the resurgence of polio, the Ebola outbreak in West Africa, and most recently the Zika virus.)

“I think it was the correct decision,” says Duane Gubler, an infectious disease specialist who recently retired from Duke-NUS Medical School in Singapore. “However, the threat is there and needs to be recognized, not ignored like we usually do.” 

Yellow fever is caused by a virus spread by Aedes aegypti, the same mosquito that spreads Zika. Isolated human cases usually occur in or close to the jungle, where monkeys are a reservoir of the pathogen. When the virus gets into the mosquito population of a major city, however, it can cause devastating outbreaks. This happened in December of last year in Luanda, the capital of Angola and home to at least 8 million people. In the country as a whole, 2267 suspected cases of yellow fever have been reported, with at least 293 deaths.

“Urban yellow fever is a particularly dangerous and concerning situation because of the possibility of rapid spread,” Bruce Aylward, head of the Outbreaks and Health Emergencies Cluster at WHO, said at a press conference in Geneva, Switzerland, today. Indeed, the outbreak appears to have spread to Kinshasa, another African capital with millions of inhabitants. And travelers infected in Angola have also been reported in Kenya and China.

The chair of the WHO emergency committee, Nigerian virologist Oyewale Tomori, said that the affected countries need to make absolutely sure that visitors are vaccinated against the virus. He added that surveillance needs to be intensified, mass vaccinations organized, and risk communication improved.

But the crisis has eased a bit. Although an emergency stockpile of 6 million doses of yellow fever vaccine was used up earlier this year in combatting the Angolan outbreak, production is replenishing it, Aylward said. “Currently we expect that by the end of May the stockpile will be about 7 million doses.” Several million more doses should become available in the coming months.

Even if the vaccine runs low again, some scientists have argued that current doses could be split to vaccinate two or even five people instead of one each. It is unclear how long protection would persist or even by which factor to divide doses. “Right now there are gaps in the scientific knowledge,” Aylward acknowledged. But Jack Woodall, a retired virologist in London who worked at the Centers of Disease Control and Prevention and WHO, thinks lower doses should be used immediately. “They are always talking about the future and in the meantime the vaccine is getting used up,” he says. “As long as this outbreak drags on, the risk is high.”