Research in context
yellow fever, infections
DISEASE, VIRUS, YELLOW FEVER, INFECTIONS

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To our knowledge, we assessed, for the first-time, fractional doses of the yellow fever vaccine in HIV-infected adults without signs of clinical disease in coastal Kenya. The study evaluated the immunogenicity and safety of the fractional doses of the yellow fever vaccine at 10 days, 28 days, and 1 year after vaccination. The results show that fractional doses met non-inferiority 28 days after vaccination, and that protection was maintained at 1-year follow-up. 10 days after vaccination, however, seroconversion and neutralising antibody levels were significantly lower in the fractional dose arm. There were no safety concerns in this population.
The results from this study increase confidence that one-fifth fractional doses of yellow fever vaccines can be used in HIV-infected individuals. The data further support evidence-based guidelines for HIV-infected individuals. Studies evaluating the longevity of vaccine-induced immunity are needed to inform policies for wider use of the dose-sparing strategy.In Kenya, an estimated 1·3 million people were living with HIV in 2018, with about 37 000 new infections per year.WHO-prequalified yellow fever vaccines are live attenuated virus vaccines derived from the 17D strain (substrains 17DD and 17D-204 and 17D-213, a substrain of 17D-204). Vaccines are formulated to contain a minimum potency of 1000 IU per dose, but average doses are much higher than the recommended minimum.Although standard doses of the yellow fever vaccine are considered safe in people living with HIV, vaccination might result in delayed and lower rates of seroconversion and lower immunogenicity, efficacy, and herd immunity compared with HIV-negative populations.Following the preceding study assessing all four WHO-prequalified yellow fever vaccines,