Purpose
Introduction
Travel medicine is based on the concept of risk reduction. In the context of travel medicine, "risk" refers to the possibility of harm occurring during a trip. Some risks are avoidable, while others are not. For example, vaccine-preventable diseases can be mostly avoided, depending on the protective efficacy of the vaccine, whereas natural disasters, accidents, and diseases without vaccines may not be easily avoidable.
Perception of risk is a subjective evaluation of whether a risk is considered high or low; is 1 in 10,000 a high risk or a low risk? Tolerance refers to acknowledging a risk and accepting it; a risk of 1 in 100,000 might be tolerable for an individual traveler but not for another. The overall perception of risk is based on a combination of likelihood and severity. A low likelihood of a severe and untreatable disease might be perceived as more of a risk than a higher likelihood of a less severe disease.
Understanding the role of risk perception and risk tolerance is important because we rarely have exact rates of diseases in the proposed destinations, and even when we do, the rates of disease range from 1 in 500 (an estimate of the risk for typhoid fever in unvaccinated travelers to Nepal) to 1 in 1,000,000 (an estimate of the risk for Japanese encephalitis [JE] in travelers to Asia), leaving it to travelers and healthcare professionals to decide if these are high or low risks, and worth the expense and slight risk of immunizations. Additional information to help make an informed decision should include the severity of the disease, how readily the disease can be treated, and the length and type of travel. For example, the disease risks encountered by travelers on luxury African safaris might be quite different from the disease risks for people going to work in resource-poor areas of the same countries.
Even when risk is low, travelers' decisions will still reflect their perceptions and tolerance of risk. When told that the risk for JE is 1 in 1,000,000, a traveler might reply, "Then I guess I don't have to worry about it," while another might say, "That one will be me!" Each traveler will have their own ideas about the risks, benefits, and costs of vaccines and drug prophylaxis; healthcare professionals should discuss these with travelers in detail, with the goal of shared decision-making.
Statistics alone can't solve the problem. The difference between a risk of 1 in 100,000 and 2 in 100,000 may seem like double the risk, but from a practical point of view, it is not significant. As an example, the concepts of perception and tolerance of risk affect both the healthcare professional and the traveler when it comes to administering or receiving yellow fever vaccine. Due to the unique risk of becoming severely ill or dying from the vaccine, the perception of the vaccine risk and the tolerance for it falls on the practitioner as well as the traveler. Often the risk of yellow fever disease is close to the risk of the vaccine, which means that the decision may have to be made based on other factors, such as facing the risk of the vaccine at home versus the uncertain risk of being in a yellow fever zone without being vaccinated.
Being aware of the concepts of perception and tolerance of risk as two separate entities helps facilitate shared decision-making with the traveler. Travel medicine is not just a menu of items to check off when it comes to low-risk and high-consequence diseases (such as JE) or even just a low risk of a less consequential disease (such as typhoid fever). By helping travelers discover how they feel about risk, as discussed above, travelers on the same or similar itineraries can make different decisions about the need for immunizations or prophylaxis. Perception ("is there a high risk or not?") and tolerance ("is that a risk I'm willing to take?") create a framework for shared decision-making.
The COVID-19 pandemic taught us many lessons. One important lesson is the impact a pandemic can have on travel itself, with quarantines, flight cancellations, and testing and vaccine requirements. Calculating the risks and benefits of travel during a pandemic still calls upon the individual to take into account their perception and tolerance of risk. Figuring out whether travel is even safe or wise has become the most prominent decision people need to make when pandemic disease is present, often with no easy answers. What is true this week can be completely different a week later.