Perspectives: Why Guidelines Differ


Numerous international, national, and professional organizations publish guidelines and recommendations for travelers, including the CDC Yellow Book. Travel health providers should be aware of these recommendations, even though they may not follow them in every instance. This way they can explain to their patients how their recommendations, and their patients’ choices, may be at odds with what others recommend. It can be unsettling for patients to receive travel medicine advice, vaccines, or an antimalarial drug prescription from a provider, only to find that what has been advised or prescribed is contradicted by what other professionals, friends, or destination-country nationals have to say. The skillful travel health provider will be able to help the traveler reconcile seemingly conflicting advice.

How Guidelines Are Created

In the United States, the Food and Drug Administration (FDA) approves standards for how to use a vaccine or medication, including dosages, ages for which the product is approved, and booster recommendations. Recommendations about when to use a product may come from a separate body, such as the Advisory Committee on Immunization Practices (ACIP). To give ACIP the best possible information on which to base their recommendations, working groups of experts may hold meetings to review the literature and new studies. CDC Yellow Book travel advice will always be compatible with ACIP recommendations but may, on occasion, offer country- and situation-specific guidelines for vaccine use.

International organizations such as the World Health Organization (WHO) and national committees of other countries, as well as medical organizations such as the International Society of Travel Medicine (ISTM) or the Infectious Diseases Society of America, may each promote their own sets of guidance. Other professional organizations may create consensus clinical practice guidelines based on published medical literature and expert opinion. Travel medicine–specific paid subscription services employ travel medicine experts to organize and present guidelines for health care providers who see international travelers in their practice but who may lack expertise in the subject. Guidance provided about vaccines and malaria prophylaxis can differ from CDC advice.

Guidelines put forward by different countries and organizations may differ in substantial ways. Reasons for this include differing licensure and availability of products, cultural perceptions of risk, lack of definitive evidence, and differences of opinion among experts.

Availability of Products

Travel health providers can only use the products available to them. Availability is determined by the regulatory approval status of the product and, to a lesser extent, the marketing and distribution plan of the manufacturer. Regulatory approval processes vary greatly by country. For example, registering a new vaccine or antimalarial drug in the United States is a costly and rigorous process. If the market in a particular country is insufficient to justify the expense of registration, a commercial company may not seek it.

Standards for licensure also vary. What may be sufficient for one regulatory authority may not suffice for another. For example, primaquine, an option for malaria prophylaxis in the United States, is not registered or commercially available in Switzerland. Atovaquone-proguanil was available for malaria prophylaxis in the United States before many other countries. Four Japanese encephalitis vaccines are available in the world, but only 1 is licensed in the United States.

Even when the same products are available, recommendations for use may not be the same in all countries. The injectable capsular polysaccharide typhoid vaccine and the oral typhoid vaccine are examples. In the United States, a booster of the polysaccharide vaccine is recommended after 2 years, but in most European countries, a booster is recommended after 3 years. In the United States, a packet of 4 oral typhoid vaccine capsules is dispensed, whereas in Europe, 3 doses are considered adequate. The regulatory agencies may have reviewed the same data and drawn different conclusions, or they may have reviewed different data at separate times. Regulatory submissions to various agencies rarely occur at the same time; therefore, the data available for review by each agency may not be the same, for legitimate reasons.

Perception of Risk

People from varying backgrounds can view the same risk data and come to very different conclusions as to the cost and benefit of minimizing that risk to what they consider to be an acceptable level. For example, recommendations to prevent malaria during travel to India vary widely. Germany does not recommend using standard prophylaxis for any travel to an Indian destination; standby emergency treatment (SBET) or self-treatment) only is the recommendation for identified risk destinations. Guidelines from the United Kingdom recommend only awareness and mosquito bite prevention for more than half the Indian subcontinent, including large cities and popular tourist destinations in the north and south, while suggesting prophylaxis consideration for some travelers or for those visiting higher-risk areas. By contrast, CDC recommends malaria prophylaxis for any Indian destination (except for some mountainous areas of northern states) for all travelers.

Lack of Evidence

In many cases, limited or no data are available to inform an evidence-based assessment. Travel health providers must then defer to expert opinion or extrapolate from limited data in conjunction with expert opinion. In travel medicine, it is rare to have numerator and denominator data on the risk of any disease. For example, any new data on the risk of hepatitis A in travelers would have to account for the high immunization rate with hepatitis A vaccine. Because such data are rarely available, travel health providers often rely on historical data that captured few actual cases.

Can We Harmonize Guidelines?

The complex nature of how health organizations obtain, evaluate, and verify data, combined with fundamental differences in risk perception, makes it likely that multiple, overlapping, and at times conflicting guidelines will continue to exist. However, conflicting guidelines have decreased in the past decade due to the efforts of several organizations. A recent example has been the collaboration among the WHO, US CDC, and the European Centre for Disease Prevention and Control (ECDC) to develop consistency and clarity in defining the risk of Zika infection for travelers so that providers can more clearly relay traveler risk, particularly to those who are pregnant or planning pregnancy.

In summary, the role of the travel health provider is to understand the various differences in guidelines, interpret this information, and convey tailored and informed advice in an assured and comforting manner to travelers.


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David R. Shlim


Perspectives sections are editorial discussions written to add depth and clinical perspective to the official recommendations contained in the book. The views and opinions expressed in this section are those of the authors and do not necessarily represent the official position of CDC.