In March 2013, the World Health Organization (WHO) Strategic Advisory Group of Experts on Immunisation (SAGE) considered a number of issues in order to update the WHO Position Paper on Yellow Fever (2003). A key conclusion of this review was that a single dose of yellow fever (YF) vaccine appears to confer life-long protection against YF disease, and that a booster dose of YF vaccine is not needed to maintain immunity. While the efficacy of YF vaccine in the majority of vaccine recipients is not in doubt, the WHO announcement is somewhat surprising as there are some limitations in the evidence base, but more importantly, this announcement is not accompanied by any imminent change in the International Health Regulations 2005. The tension between what is considered best clinical practice and the law will be difficult to reconcile for many health professionals, travellers, and the travel industry, in an area of travel medicine that is already subject to debate and confusion. This commentary reviews the recent WHO announcement, and considers the practical implications for health professionals providing YF vaccine to international travellers.