Vaccine-preventable travel health risks: what is the evidence--what are the gaps?

BACKGROUND: Existing travel health guidelines are based on a variety of data with underpinning evidence ranging from high-quality randomized controlled trials to best estimates from expert opinion. For strategic guidance and to set overall priorities, data about average risk are useful. The World Health Organization (WHO) plans to base future editions of "International Travel and Health" on its new "Handbook for Guideline Development." METHODS: Based on a systematic search in PubMed, the existing evidence and quality of data on vaccine-preventable disease (VPD) risks in travelers was examined and essentials of vaccine efficacy were briefly reviewed. The Grading of Recommendations, Assessment, Development and Evaluation (GRADE) framework was used to evaluate the quality of the data. RESULTS: Moderate-quality data to determine the risk of VPD exist on those that are frequently imported, whereas in most others the level of confidence with existing data is low or very low. CONCLUSIONS: In order for the WHO to produce graded risk statements in the updated version of "International Travel and Health," major investment of time plus additional high-quality, generalizable risk data are needed.