Active Infection & Immunity Pregnancy, Children & Inherited Conditions

Extending Trials of fractional doses of yellow fever vaccine for policy impact

Funder Wellcome Charity-funded
Associated organisations Epicentre · KEMRI-Wellcome Trust Research Programme · Ukri-Mrc Europe PMC affiliations are not treated as award recipients or mapped locations.
Funding £1.3M
Period Nov 2024 — Oct 2027

In plain English

AI plain-English summary

A single dose of yellow fever vaccine, when given at one-fifth the standard strength, may protect people for years—but no one yet knows for sure how long that protection lasts. This matters because yellow fever kills 20 to 50 percent of those infected, and over 100,000 cases occur annually in Africa alone. The vaccine is difficult to manufacture quickly, so global supplies are chronically short. During outbreaks, the World Health Organization already recommends using fractional doses to stretch existing stocks, but the durability of that immune response beyond a few years is unknown. The researchers will measure yellow-fever-neutralising antibodies in adults and children in Kenya, Uganda, and The Gambia who received either a fractional or standard dose two to six years ago in earlier trials. A single blood sample from each participant will show whether fractional dosing provides lasting immunity comparable to the full dose. If fractional doses prove durable, the WHO could recommend them not just for outbreak control but for routine vaccination programmes. That would effectively multiply vaccine supplies several-fold without increasing production, making it easier to protect populations across Africa and South America. The data will also clarify whether booster doses are needed.

View original technical description
Yellow fever (YF) is a zoonotic mosquito-borne viral disease endemic in Africa and South America. Over 100,000 YF cases are estimated to occur annually in Africa which, with a case fatality of 20-50%, represents a major risk to public health. A single dose of licensed YF vaccines provides life-long immunity. However, the vaccine manufacture process is laborious and difficult to scale up rapidly, leading to persistent challenges with global vaccine availability. Fractional dosing with YF vaccines has been adopted by the World Health Organization (WHO) as a strategy to control YF outbreaks, but the durability of the protective immune response following fractional dosing remains unknown. We will address this question by measuring YF neutralizing antibody levels in adults and children who participated in randomized controlled trials of fractional versus standard doses of YF vaccine in Kenya, Uganda and The Gambia. A single cross-sectional sampling of these populations will provide immunogenicity data at 2 to 6 years since the initial vaccination with either fractional or standard vaccine dose. The data from this study will inform WHO recommendations on the use of fractional doses of YF vaccines, including informing decisions on whether a booster dose is needed to maintain long-term protection.

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Researchers

Ed Clarke (EPMC Awardee)George Warimwe (EPMC Awardee)Valerie Briand (EPMC Awardee)

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Original classification

Discretionary Award

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