Health officials in Congo are preparing for a major yellow fever vaccination campaign later this month in hopes of halting the spread of the disease before it creeps into the capital, a possibility that has sparked fears of a much wider epidemic.
To stretch limited global supplies of the vaccine, officials in the capital, Kinshasa, plan to use a smaller dose than normal, a proposal that has been endorsed by both the World Health Organization and Congo’s health ministry.
But a WHO official told STAT that authorities have considerable work to do before they can set a formal date for the vaccination campaign: securing enough special syringes to deliver a far smaller dose of vaccine, training health workers, and finalizing a public education program.
If people do not believe the lower dose — one-fifth the normal dose — will be effective, they are likely to try to get vaccinated more than once, putting further strain on supplies.
“I think we need to think about everything,” said Dr. William Perea, the WHO’s coordinator for control of epidemic diseases unit. “You can never be careful enough.”
The Congolese health minister, Felix Kabange, said last week the campaign will include everyone in Kinshasa as well as some people in the provinces of Kwango, Lualaba, and Kasai.
Currently, the nearly 2 million residents of the capital of the Republic of Congo, Brazzaville — just across the Congo River from Kinshasa — are not scheduled to be vaccinated.
“We are trying to do Kinshasa to avoid Brazzaville,” said Perea.
The goal is to get the job done as quickly as possible once the work actually starts, so as to not paralyze other heath activities in the country. Perea said officials hoped to complete the vaccination campaign within two to three weeks.
“That will be challenging, but possible,” he said.
The yellow fever virus is normally found in forested parts of Africa and South America, where it is transmitted between monkeys and mosquitoes. But it occasionally breaks out of the transmission cycle and starts to infect humans.
It is spread by Aedes mosquitoes — the same mosquitoes that transmit the Zika virus.
People who contract the virus experience fever, headache, backache, muscle pain, loss of appetite, and nausea, or vomiting. The symptoms typically last three or four days.
But after an apparent recovery, about 15 percent of people experience a relapse that spirals them into a second, more severe phase of the illness during which they can develop jaundice. Roughly half of people who develop a toxic phase die, the WHO estimates.
Yellow fever has spread into Congo from neighboring Angola, where an outbreak in the capital, Luanda, has expanded to all 18 provinces of the country. The need to mount mass vaccination efforts in Angola has put enormous pressure on the world’s supplies of yellow fever vaccine.
An emergency stockpile of 6 million doses of yellow fever vaccine has previously been more than sufficient to quell outbreaks that would flare up.
The stockpile is maintained and managed by the WHO, UNICEF, the International Federation of the Red Cross, and Doctors Without Borders. It is paid for by Gavi, the Vaccine Alliance, an international organization that uses private and public money to subsidize vaccination programs for the world’s poorest countries.
But so far this year, 19.6 million doses have been delivered or promised through the stockpile. And the outbreaks are still underway.
Congo has reported 1,307 suspect and 68 confirmed cases, with 75 reported deaths so far. Many of the cases are imported from Angola; there is substantial movement between the countries.
Vaccination efforts have been concentrated along the countries’ shared border. But a few locally acquired cases in Kinshasa and the fear that the virus could take off in that teeming city — population at least 11.6 million — led to the conclusion Kinshasa should be vaccinated.
Global supplies aren’t adequate to give everyone there a full dose. So the WHO’s expert panel on vaccinations has agreed that fractional doses can be given to anyone above 2 years of age.
Several studies have suggested smaller doses of the highly effective yellow fever vaccine can still protect against infection. But it’s not known how long that protection will last or whether it will be as protective for infants as it is for adults.
So the expert panel recommended everyone who is given a fractional dose should later get another, regular-sized shot as a booster dose. With a regular dose of yellow fever vaccine, one injection is thought to protect for a lifetime.
The expert panel also advised that a full dose be used for children under the age of 2.