In this edition of Academia Meets Life, I cover an article which looks at the gaps in what we know about vaccine preventable diseases in travelers. While most–or maybe many–travelers go to their medical providers to receive appropriate vaccines before traveling, there are certainly those that either don’t or choose not to. But how to the providers decide what to recommend?
(In the United States, the Centers for Disease Control and Prevention [CDC] provide guidance based on similar criteria as those described here. This guidance is at the international level.]
This article specifically reviews how vaccine recommendations are made, and what gaps exist in the knowledge base used to make these recommendations. The authors focus on the absence of a current edition of the World Health’s Organization handbook for travel medicine, and what would be needed to create an evidence-based handbook in the future.
How recommendations are made: Randomized controlled trials, expert consensus, and estimates on disease (plus some guesswork, I think) are all involved in creating health guidelines for vaccines for travelers. Ideally, there is disease incidence information (rates of disease within a population) for both travelers and the native population.
What we don’t know: Unfortunately, there is rarely data between different types of travelers. I.e. those going for business, those visiting family, or those working or playing in high risk situations (i.e. health care environments). Because there are not data on these different groups, recommendations are typically far from individual.
What existing literature says: There are certainly studies focused on vaccine-preventable diseases in travelers. The authors focus on travelers from industrialized nations. However, the methods of data used to collect the information in travelers was incredibly varied–from voluntary reporting to anecdotal reporting. In other words, some of the methods of data collection, while better than nothing, are far from ideal. Moreover, the consistency within the literature on specific diseases is not so good. In other words, the existing evidence is spotty for most vaccine preventable diseases in travelers.
Part of the problem in tracking this type of information is travel, in and of itself. Where you acquire a disease, where you get treated for that disease, and where you consider your location of permanent residence are often three different places. The systems to track this information often require voluntary reports–from you, from the treating provider. Reporting chains frequently are disconnected or break down.
What are the most common diseases in travelers? Well, this article claims travelers diarrhea, influenza, and Hepatitis A top the list (estimated at between 1-10 travelers per 10,000 in a month). But given that the data is pretty bad, I’m not totally certain how sure we should be about these rankings of disease risk, but nonetheless…. The next set of common diseases (estimated at between 1-10 travelers per 100,000 in a month) are Hep B, typhoid, rabies, tick-borne encephalitis, and tuberculosis. You’ll see “vaccine-preventable” is used loosely, as many of the diseases they discuss do not have licensed vaccines in the United States or have insufficient evidence regarding their efficacy.
For all you that have had the Yellow Fever vaccine, you’ll be interested to know this was in the very last category of risk (estimated <1 traveler per 100,000 in a month).
In sum: To no one’s surprise, the authors state that additional research is needed to better inform recommendations, including on traveler activities, seasonal impacts, and prevention of these diseases by non-vaccine measures.
My take: I think additional research is almost always needed on almost everything. The question is, how to get it done–in a reliable and valid way–that actually increases knowledge. And who pays for it. I’m guessing with disease rates this low, this is not a particularly high research priority, particularly given the myriad of other disease issues which deserve higher priority. While it’s important to base recommendations on scientific evidence, sometimes you have to make recommendations on the best information available–not the information you wish was available. Hopefully a chat with a good travel medicine professional–coupled with a dose of common sense–can help us all make appropriate decisions about vaccines for travel.
ALSO hey give an example of “copious” washing of any bite with soap and water to prevent rabies…while this can help (the CDC agrees), I’d really suggest you follow the CDC guidelines for rabies rather than just relying on soap and water as the quick fix for a disease that is, for all intents and purposes, 100 percent fatal. Just saying.
Source: Steffen, R, Behrens RH, Hill DR, Greenaway C, & Leder, K. 2015. “Vaccine-Preventable Travel Health Risks: What Is the Evidence–What Are the Gaps?” Journal of Travel Medicine. 22(1): 1-12.
Great advice guys!