Via Science, Kai Kupferschmidt writes: Yellow fever emergency forces officials to combat virus with tiny dose of vaccine. Excerpt:
It’s an unprecedented emergency measure, but one that could become the norm: In a bid to stop an outbreak of yellow fever, more than 8 million people in Kinshasa, the capital of the Democratic Republic of the Congo (DRC), will be vaccinated using just one-fifth the normal dose. The campaign, scheduled to start next week, comes as yellow fever continues to spread in the DRC and vaccine demand outstrips supply.
Scientists feel confident that the lower doses will offer protection, at least for the short term, but they are urging studies accompanying the campaign to assess whether routine use of the lower dose is an option.
The current outbreak started in neighboring Angola in December of last year and later spread to the DRC. According to the World Health Organization (WHO), more than 16 million people in the two countries have already been vaccinated, and Angola has reported no new cases for more than 6 weeks. But new cases are still emerging in the DRC, which has reported more than 2000 suspected cases so far and 95 deaths.
WHO's emergency stockpile of yellow fever vaccine, which was depleted earlier this year, has been restocked and is now back to 5 million doses. But the Congolese government, worried that the virus could spread rapidly among Kinshasa's 10 million residents, has decided to stretch the 1.7 million doses it has received by giving people 0.1 milliliters of the vaccine each instead of the standard 0.5 milliliters.
The yellow fever virus is primarily transmitted by Aedes aegypti, the mosquito species that also spreads Zika and dengue. Most people who are infected have no symptoms, but about 15% develop serious disease, and about half these patients die. There is no cure, but the vaccine, although cumbersome to produce, is highly effective: A single dose confers lifelong protection.
Fearing that the disease could spread to Asia, which has never seen a yellow fever outbreak, some experts had urged governments and WHO to adopt the vaccine-saving strategy. In June, WHO's Strategic Advisory Group of Experts (SAGE) on Immunization concluded that the lower dose would still offer protection for at least 12 months. (The recommendation was made in an emergency session, but the group has planned a formal evaluation for October.)
“We felt very comfortable with the data that was presented to go ahead and make the recommendation,” says SAGE chair Jon Abramson, a pediatrician at Wake Forest School of Medicine in Winston-Salem, North Carolina. “We feel the benefit of vaccinating as many people as we can far outweighs the small risk that somebody won’t respond who could have responded to a larger dose.”
