1. This ten-year follow-up study of a randomized controlled trial suggested that intradermal administration of one fifth of the yellow fever vaccine could provide long-term immunity for at least ten years.
2. The participants in this study who received the fractionated dose of yellow fever vaccine did not require any booster vaccines to maintain immunity during the study period.
Evidence Rating Level: 1 (Excellent)
Study Rundown: Yellow fever results in acute hemorrhagic disease, which is caused by a virus transmitted through mosquitoes. This infectious disease is endemic in many tropical and subtropical areas, especially in parts of Africa and South America. Prophylaxis is the mainstay of treatment and prevention for yellow fever, as there is not currently a cure beyond supportive care for those who contract the disease. As the yellow fever vaccine is challenging to make in large doses, many countries do not have adequate stores of the vaccine in case of an outbreak. Therefore, the authors of this study examined whether fractional-dose vaccination could confer long-term immunity. Generally, they observed that fractional-dose vaccination offered long lasting protection against yellow fever. Study limitations included that only 48% of the participants from the original trial then participated in this follow-up study. Furthermore, the authors acknowledged that the study did not compare methods of vaccination with the yellow fever vaccine, such as evaluating subcutaneous versus intradermal injection.
Relevant Reading: Fractional-Dose Yellow Fever Vaccination — Advancing the Evidence Base
In-Depth [randomized controlled trial follow-up]: The authors of this study conducted a ten-year follow up of a randomized controlled non-inferiority trial, which included about 48% of the original study participants. This study was based in the Netherlands; a total of 75 participants provided a blood sample for the study. The authors assessed virus-neutralizing antibodies in patients who received the fractionated dose of yellow fever vaccine compared to the full dose through a plaque reduction neutralization test. The secondary end point of the study was the geometric mean titer (GMT) of virus-neutralizing antibodies in each group. The mean age of vaccination for both groups was 26 and both had the same mean time since primary vaccination. Generally, the authors observed that 98% of the fractionated-dose group had protective levels of yellow fever-neutralizing antibodies (95% CI, 89% to 100%) compared to 97% (CI, 97% to 100%) in the standard-dose control group. Furthermore, similar GMTs were observed between the fractional and standard-dose groups.
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